Atlanta, Georgia: Over 22 states will hold contests on February 5, also known as Super Tuesday, and the outcome could whittle down the nominees for both parties.
Delegate-rich states such as California, New York and New Jersey could be make-or-break contests for both Republicans and Democrats.
Sen. John McCain of Arizona, fresh off crucial wins in the South Carolina and Florida primaries and important endorsements from the Los Angeles Times, former GOP presidential candidate Steve Forbes and former New York City Mayor Rudy Giuliani, will go head-to-head with the competitive candidate and former governor of Massachusetts, Mitt Romney.
SUPER TUESDAY: Delegate-rich states such as California, New York and New Jersey could be make-or-break contests for both Republicans and Democrats.
Romney, who has the campaign war chest to compete well beyond Super Tuesday, will be a formidable force against the Arizona senator in several delegate-rich states.
The ad wars between McCain and Romney are also heating up. Both candidates are reportedly spending seven-figure amounts in several Super Tuesday states.
California is a crucial win state for either party's candidates. At stake for Republicans: 170 delegates - a figure that makes up 14.3 per cent of delegate votes needed to win the nomination. For Democrats, the winner will take home 370 delegates.
McCain, who received an endorsement from California Gov. Arnold Schwarzenegger, could truly benefit. In the Florida primary, exit polls showed that Gov. Charlie Crist's endorsement helped McCain win the contest.
Other GOP candidates in the race - Mike Huckabee and Texas Rep. Ron Paul -- face an uphill challenge money-wise and momentum-wise.
Huckabee's evangelical support could, however, help him in Southern and midwestern states such as Georgia, Missouri, Arkansas, Oklahoma and Kansas.
The Democratic race, meanwhile, remains extremely tight going into Super Tuesday.
Fresh off Thursday's calm and cordial Democratic debate at the Kodak Theatre in Los Angeles, California, Sens. Hillary Clinton of New York and Barack Obama of Illinois appear to be headed for a decisive match - though both candidates say they will campaign far beyond the February 5 contests.
Obama won the season-opening Iowa caucuses, then finished second to Clinton in every contest until last week's South Carolina primary - which he won with a commanding 55 per cent of the vote in a three-way race.
On Friday, the Illinois senator received the endorsement of the Los Angeles Times, one of the largest newspapers in the country.
Clinton scored victories in the New Hampshire primary and Nevada caucuses.
She also was the top vote getter in Florida and Michigan, although no Democrats campaigned in those states and their delegates to the nominating convention will not count because of a squabble between state and national party leaders over the timing of the primaries.
And John Edwards' support to either candidate could send Clinton or Obama over the edge, delegate wise.
A win for either party's nominees in Super Tuesday states like California and New York - two states with uber expensive media markets - will require significant cash.
The Super Tuesday states include Alabama, Alaska, American Samoa, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Georgia, Idaho, Illinois, Kansas, Massachusetts, Minnesota, Missouri, Montana, New Jersey, New Mexico, New York, North Dakota, Oklahoma, Tennessee, Utah, West Virginia
Alabama has not voted for a Democratic presidential candidate since 1976, when Jimmy Carter beat Gerald Ford by 13 points.
George W. Bush carried Alabama in a landslide in 2004, beating John Kerry by over 25 points.
Alabama's large African-American minority is the Democratic Party's base. Democrats gain much of their institutional strength from the state's well-organized teachers' union and trial lawyers.
White evangelical Protestants and affluent young white families in the suburbs make up the base of the Alabama GOP. Much of the party's institutional support comes from the state's business owners.
Alaska is a safe Republican state. It has voted for a Democratic presidential candidate only once since gaining statehood in 1959.
Since becoming a state, Alaska has never held a presidential primary, choosing rather to hold caucuses.
The most Democratic regions in Alaska include the state's southeast panhandle, which includes Juneau, and the vast area in the North and West, sparsely populated by Native Americans and Aleuts.
The area around Anchorage and Fairbanks tends to go Republican.
While American Samoa participates in the Democratic and Republican nomination processes, it does not participate in the general election.
In Arizona, Latinos are an important -- and growing -- voting bloc. In the 2004 Democratic primary, they constituted 17 percent of the entire electorate. In the 2004 general election, they made up 12 per cent of the electorate and favored Sen. John Kerry over Bush.
Maricopa County, which includes Phoenix, is home to over 60 per cent of Arizona's registered voters. Largely white collar and home to a sizeable high-tech economy, the county usually tilts Republican, though Democratic votes can be found in the university community of Tempe and Phoenix's Latino community.
Pima County in the southern part of the state often goes Democratic because nearly 25 percent of the population there is Latino.
Sparsely populated areas in the northern part of the state, meanwhile, have increasingly leaned Republican recently.
A slight plurality - 51 per cent - of Arizona's Democratic primary electorate in 2004 was composed of self-described moderates or conservatives.
Even though McCain handily won his home state's primary in 2000, he defeated Bush by only 7 points (51 per cent to 44 per cent) among the 62 per cent of GOP primary voters who described themselves as conservatives. Bush beat McCain by 16 points (54 per cent to 38 per cent) among the 24 per cent of primary voters who called themselves "very conservative."
While Arkansas can be a Republican-friendly state, Democrats like Sens. Mark Pryor and Blanche Lincoln, as well as current Gov. Mike Beebe, have found success in recent years.
The state tends to vote Republican in presidential elections, except in cases when a Southern Democrat, such as Bill Clinton, appears on the ticket. President Bush carried the state in 2004 by almost 10 per cent.
Huckabee was only the third Republican to serve as governor of Arkansas since Reconstruction.
Arkansas is the smallest state between the Mississippi River and the Pacific Ocean. In terms of population, it's the smallest state in the South.
The last time California played a critical role in the primary season was in 1972, when George McGovern's 5-point victory over Hubert Humphrey helped solidify the senator's hold on the Democratic nod.
The last time California was critically important on the GOP side was in 1964, when Barry Goldwater squeezed out a narrow victory over Nelson Rockefeller. Goldwater went on to win the Republican nomination.
John Kerry won every county in the 2004 primary. Bill Clinton, former Vice President Al Gore and John Kerry all carried California by solid margins.
While California has a reputation for being heavily Democratic, mainly due to large metropolitan areas such as Los Angeles and San Francisco, the state also has a long history of supporting Republicans, especially for governor. Ronald Reagan became president after he was governor of the state, and Schwarzenegger currently holds the title.
California's economy is larger than all but four nations, having surpassed France in 2002.
With so many electoral votes at stake, pundits say the state is crucial to picking either party's nominee for president.
Colorado tends to vote Republican in presidential elections. The GOP presidential candidate has carried Colorado in 12 of the last 14 presidential races dating back to 1952. The only exceptions came in 1964 and 1992, when the state supported Lyndon Johnson and Bill Clinton, respectively.
Denver, Adams and Boulder counties in central Colorado are the most Democratic areas of the state. The eastern and western borders are heavily Republican.
Democrats believe the rising political strength of the Latino community will make the state more competitive.
Self-identified members of the religious right made up roughly one-quarter - 26 per cent - of the Republican primary electorate in 2004. Self-identified conservatives made up 63 per cent of the Republican primary electorate in 2004.
In late August, Democrats will flock to Denver for the Democratic National Convention.
Connecticut has recently become a Democratic stronghold in presidential politics. The Democratic presidential nominee has carried the state by double-digit margins in each of the last three elections.
The most Democratic areas of the state include areas around Hartford, New Haven and Bridgeport. The GOP-favored areas are the eastern and western coastal regions. Connecticut Republicans, however, tend to be very moderate by GOP standards.
Connecticut has the highest per-capita income in the nation as of 2007.
A majority of voters in the 2000 GOP primary were either self-described moderates or liberals. John McCain won the state's primary by beating Bush among both of these groups of voters.
One of Bill Clinton's few defeats came during the 1992 primary, where he was narrowly beaten by Jerry Brown, 37 per cent to 36 per cent.
For half a century, Delaware was considered one of the best bellwether states in presidential politics. From 1952 to 2000, it picked the winner of the popular vote in every presidential election. The streak was broken in 2004, when the state voted for Kerry by a margin of almost 8 per cent.
Delaware only has three counties -- Kent, New Castle and Sussex. New Castle County includes heavily Democratic Wilmington and a number of more GOP-leaning suburbs.
Georgia has voted Republican in five of the last six presidential elections.
The last Democrat to carry Georgia in a presidential election was Bill Clinton in 1992. Georgia was the only Southern state to support Jimmy Carter in his 1980 White House bid against Reagan.
African-Americans made up 47 per cent of Georgia's 2004 Democratic primary electorate.
From 1990 to 2004, Georgia's population grew by 36 per cent. This was the sixth-highest rate of population growth in the United States, and the highest rate for any state east of Colorado. The 2000 Census recorded Georgia as the tenth-largest state -- the first time it has been in the top 10 since the Census of 1850.
Georgia has more African-Americans than any other state except Texas and New York, and could soon surpass them -- something that could be favorable to Obama, who garnered high numbers of African-American voters in his South Carolina primary win.
Atlanta and its inner suburbs are the most solidly Democratic regions of the state. Historically, Democrats have also run well in the central part of the state. On the flip side, Atlanta's ring of outer suburbs is the most heavily Republican part of the state.
Idaho holds its Democratic caucuses on February 5.
It is one of the most reliable Republican states in the nation. In 2004, Bush defeated Kerry in the state by 38 points -- Bush's third-highest margin of victory in any state.
Lyndon Johnson was the last Democrat to carry Idaho in a presidential election, beating Barry Goldwater by less than 2 per cent in 1964.
Obama's home state of Illinois has increasingly become a Democratic stronghold in presidential politics. Democrats have fared better in Illinois than nationwide in every election since 1980.
Historically, the so-called "Collar Counties" of the Chicago suburbs - five in all - make up one of the most fiercely contest battlegrounds in the state.
Republicans traditionally did well here, especially in the more affluent areas, but as the GOP shifted rightward in the 1980s on social issues such as gun control and abortion, Democratic support began to rise.
Downstate, communities such as Peoria, Rockford and Springfield are also targeted because of their sizable working-class, swing constituencies.
Kansas, meanwhile, holds Democratic caucuses. The state is traditionally a Republican stronghold.
Despite its rural image, Kansas' population increasingly lives in a metropolitan area. A slight majority of Kansas residents now live in five counties, which include Kansas City, Lawrence, Topeka and Wichita.
Between 2000 and 2004, the state's population declined in 78 of the other 100 counties.
Hispanics are a growing political voting bloc. A large number of Latinos now work in meatpacking factory towns, and Hispanics accounted for nearly half of Kansas' population growth in the 1990s.
The most Democratic area is in Kansas City, as well as the state capital, Topeka. The Republican base is in the suburbs of Kansas City and the state's rural western counties.
Massachusetts is a major Democratic stronghold. No Republican has carried the state in a presidential election since Reagan narrowly defeated Walter Mondale in 1984.
Romney served only one term in Massachusetts. In this 2008 primary race, Romney's home newspaper, The Boston Globe, endorsed McCain.
Massachusetts Republicans tend to favor perceived moderates in presidential primaries - such as Nelson Rockefeller, Gerald Ford and George H.W. Bush.
In terms of an overall share of the vote, Massachusetts was McCain's best state in the 2000 primaries, beating Bush by 33 points.
Minnesota, long seen as a bastion of liberalism, has become much more of a battleground recently. The state's often-unpredictable voting patterns propelled several liberal state candidates.
Minnesota has also become much more closely contested in presidential campaigns, tilting narrowly Democratic in 2000 and 2004.
No Republican since Richard Nixon in 1972 has carried the state in a presidential general election. This is the longest Democratic streak of any state in the nation, not counting Washington DC.
Minnesota Democrats generally run strong in Minneapolis-St. Paul, as well as in the state's northern counties. Republicans tend to do well in the western suburbs of Minneapolis-St. Paul, as well as around Rochester and western areas of the state.
Missouri is one of the nation's most reliable bellwethers in presidential politics. For the last century -1904 to 2004 - it has voted for the winning presidential candidate in every election but one: going for Adlai Stevenson over Dwight Eisenhower in 1956.
The state's Democratic base is around urban areas such as St. Louis and Kansas City. Republicans tend to rely on strong support from the more rural central portion of the state, including Springfield and Jefferson City, the state capital.
Strong union support is an important factor for Democrats. Almost four in 10 voters in the 2004 Democratic primary came from a household where someone belonged to a union.
Sixty percent of voters in the 2004 Democratic primary were self-described moderates or conservatives.
Almost a quarter of all voters in the 2000 GOP primary were self-described members of the religious right; 56 percent were self-described conservatives.
Montana holds Republican caucuses on Super Tuesday.
For many years, Montana was one of the most Democratic states in the Rocky Mountain West, electing only Democratic senators from 1952 to 1988. The last Democratic presidential candidate to carry the state was Bill Clinton in 1992.
The last time Montana played a role in a serious Republican nomination fight was 1976, when Reagan challenged President Gerald Ford.
Democrats benefit from strong unions in the state.
Geographically, the Democratic base is around the mining cities of Butte and Anaconda, Missoula, Great Falls, and the state capital, Helena. Billings, along with the rural east and west, tends to go Republican.
Through the 1980s, New Jersey was generally considered one of the more Republican-leaning larger states. George H.W. Bush carried the the state by 14 points in 1988. But by the mid-1990s, the New Jersey voters had become increasingly disenchanted with the more socially conservative agenda of the GOP's Southern leadership.
The state has now voted Democratic in four straight presidential elections.
New Jersey is an expensive state to contest politically, because its two largest media markets -- New York and Philadelphia - are among the nation's largest and most expensive and are outside the state.
In the past, the state's late primary - held in June - didn't help New Jersey play a significant role in the primaries. But this year, the state moved up its primaries to Super Tuesday and will more than likely be a competitive state for both parties.
New Mexico will hold its Democratic primary on Super Tuesday.
The state has historically been a presidential bellwether, siding with the winner of the popular vote for president all but once since becoming a state in 1912. In 1976, it voted for Ford over Carter.
New Mexico is also considered a swing state by both parties.
Currently, Democrats have a strong base in the north, from Latinos and newcomers in Santa Fe and Taos. Albuquerque has been politically marginal as its migrants have been culturally conservative but economically liberal. Southeast New Mexico is strongly conservative and Republican. The southwest part of the state, however, is more Latino and marginally Democratic.
New Mexico has the highest proportion of Latinos in the United States -- something that could bode well for Hillary Clinton, who garnered a large swath of Latino voters in the Florida primary and Nevada caucuses.
In New York, Hillary Clinton's home state, almost half of voters identify themselves as Democrats, illustrating that it's generally more receptive to Democrats than Republicans, though large pockets in Upstate are heavily Republican.
New York is a Democratic stronghold in presidential politics; GOP candidates have carried the state only three times in the last 12 elections (1972, 1980 and 1984).
Almost half of all voters - 49 per cent - in the 2000 New York Republican primary were either self-described moderates or liberals; 51 percent were self-described conservatives.
Over half of all voters - 52 per cent - in the 2000 Republican primary believed that abortion should be legal in all or most cases.
Thirty-six percent of New York City's residents in the 2000 Census were born in other countries, and the state has a large African-American and Latino population.
When Clinton was re-elected to the Senate in 2006, she won 83 per cent of the vote in New York City, 62 per cent in the suburbs and 60 per cent in Upstate areas. She carried 58 of New York's 62 counties, though faced a relatively unknown Republican opponent.
North Dakota may have two Democratic senators and a Democratic member of the House, but it's generally a strong Republican area. North Dakota has voted for a Democratic presidential candidate only once in the past 60 years, supporting Johnson in 1964.
North Dakota also has the lowest growth of any state since 1950.
The state is also notable in that it's the only state with no voter registration. Anyone who says he or she has lived in the state for more than 30 days can vote, but any other voter can challenge someone's residency.
Democrats do especially well in the eastern part of the state, especially around urban areas of Fargo and Grand Forks. These cities have the state's largest share of white-collar and affluent residents, and trend more Democratic than the state as a whole.
Oklahoma was once a competitive bastion for Democrats, but in recent decades, it has increasingly trended Republican.
On a presidential level, the state is now almost always an easy GOP win. It has voted Democratic only once in the last 14 presidential elections -1964.
Former Gen. Wesley Clark won the state in the 2004 Democratic nomination contest.
Sixty-nine percent of voters in Oklahoma's 2004 Democratic primary were self-described moderates or liberals. Four out of every 10 voters in the state's 2000 GOP primary, meanwhile, were self-described members of the religious right; 69 percent were self-described conservatives; and 26 per cent were moderates.
The GOP tends to run strong in Oklahoma City and Tulsa. Democrats do better in eastern Oklahoma, the poorest part of the state and home to a large Native American and modest African-American population.
Even during the heyday of the old Democratic South, eastern Tennessee leaned Republican. It continues that trend, though Democrats can rely upon small pockets of grassroots strength from African-American voters in Knoxville and Chattanooga.
Traditionally Democratic western Tennessee is now the fastest-growing part of the state, but he region's economic expansion has bolstered an increasing GOP edge.
The state's Democratic base is in the urban centers of Memphis and Nashville. The suburbs of these two cities are increasingly Republican.
Tennessee has become a Republican stronghold in presidential elections. Bush owned the state by over 14 points in 2004, and the GOP has now carried Tennessee in five of the last seven contests.
If Gore had won his home state in 2000, he would have won the White House. Instead, he lost to Bush by almost 4 points.
African-Americans made up 23 percent of the state's 2004 Democratic primary electorate. Over half of Tennessee's 2004 Democratic primary electorate was made up of self-described moderates or conservatives. Liberals accounted for 38 percent.
Roughly one out of every three voters in Tennessee's GOP presidential primary was a self-described member of the religious right.
Farther west, Utah is one of the most Republican states in the nation. The state has not supported a Democratic presidential candidate in the general election since 1964.
In six of the last eight presidential elections, the Republican presidential nominee received a higher share of the vote in Utah than in any other state.
About three-fourths of Utah's voters are Mormons, and roughly seven out of 10 Mormons vote Republican -- a factor that will undoubtedly help Romney, a member of the Mormon Church.
West Virginia will hold its Republican state party convention on Super Tuesday.
For over half a century, West Virginia has been one of the country's Democratic states. Before 2000, the state had abandoned its position of Democratic presidential standard-bearer only three times: in the GOP landslide years of 1956, 1972 and 1984.
Republicans, at least on the presidential level, have appealed to the socially conservative state based on a combination of hot-button issues such as abortion and gun control.
In a state that still depends, at least in part, on the coal industry, Republicans have also tapped into voters' concerns over the role of the environment in the national Democratic Party.
The state's union movement remains a relatively strong force, in large part due to West Virginia's coal-mining heritage.