After more than a year of campaigning, billions of dollars in ads and electioneering, two big national conventions, four race-shifting debates, and countless opinion polls, America's biggest political drama unfolds live on national TV Tuesday night. The polls are tight enough in the headline matchup, President Obama versus Mitt Romney, that nobody can say with certainty who will win (both Obama and Romney have multiple paths to victory), but there is lots of down-ticket and state-level drama to watch for, too. Here, The Week's guide to what to watch for as the votes come in, when to expect big news, and some of the options for how to watch Election Night 2012:

What's at stake?
Aside from the big race for the White House, all 435 House seats are up for grabs, as are 33 Senate seats (though only about a dozen are considered competitive). At the state level, there are 11 gubernatorial races (only four of which are truly competitive) and several notable ballot measures dealing with same-sex marriage, legalizing marijuana, and other issues with national implications.

What's the best way to watch the election unfold?
There's no lack of options. Fox starts its election coverage at 6 pm (all times are Eastern Standard); NBC, ABC, and CBS jump in at 7 pm; and PBS starts at 8 pm. On cable, CNN, Fox News, and MSNBC all begin their election specials at 6 pm, while Univision and Current TV start at 7 pm. Most of those networks, plus CSPAN, will also stream their coverage live over the internet, along with several national newspapers and politics sites. (See this guide from GigaOm for online options.) The Week will also be covering the election in real time, providing news and some instant analysis.

What to watch for, and when:
The first thing to note: Before the first polls close, there's a good chance "you'll start to see raw-total exit polls leaked," says Jonathan Bernstein at A Plain Blog About Politics. "Ignore those polls!" The exit polls are important for understanding what happened in the election, after they've been adjusted to match the final vote tallies, but they're a very unreliable gauge of how the election is panning out. "You'll know soon enough. The extra two or three hours of having an additional, very dubious, hint, just isn't worth anything."

The first concrete returns won't start trickling in until 6 pm, and the first big states don't close their polls until 7 pm. Here are some key results to watch for, in chronological order. For close Senate races, we list the final projections from four big political prognosticators — Rothenberg Political Report (Roth), Cook Political Report (Cook), Sabato's Crystal Ball (Sab), and Nate Silver's FiveThirtyEight (538) — with each projection listed as a toss-up (T), lean Democratic (LD), lean Republican (LR), safe Democratic (SD), or safe Republican (SR).

6 pm
The first polls close in Indiana and Kentucky. (In parts of both states, the polls close at 7 pm.) Romney is expected to easily win both states, but there is a competitive Senate race in Indiana, between Rep. Joe Donnelly (D) and state Treasurer Richard Mourdock (R). (Roth: T, Cook: T, Sab: LD, 538: LD

7 pm
This is when the big drama starts, as the polls close in Virginia, most of Florida, and parts of New Hampshire, three potentially decisive swing states. If the networks call Florida for Obama (unlikely: some polls in the panhandle close at 8 pm), "the chances Romney will be president drop into the single digits," say Aaron Blake and Chris Cillizza at The Washington Post. Virginia is almost as important for Romney. If Obama loses both, all eyes turn to Ohio.

Virginia is also home to one of the tightest Senate races in the country, between former Gov. Tim Kaine (D) and former Sen. George Allen (R). (Roth: T, Cook: T, Sab: LD, 538: LD

7:30 pm
and North Carolina close. Obama won North Carolina in 2008, but is the underdog this year. "Ohio is the single most important state for the electoral math of both Obama and Romney," say The Washington Post's Blake and Cillizza. "With it, Obama is close to unstoppable as long as he doesn't lose longtime Democratic presidential strongholds like Minnesota, Michigan, or Pennsylvania." If Romney takes it, "the race heads west" to Iowa, Colorado, and Nevada. 

Ohio also hosts the tightening Senate race between Sen. Sherrod Brown (D) and challenger Josh Mandel (R). (Roth: LD, Cook: LD, Sab: LD, 538: SD) "A Mandel victory is entirely dependent on Romney winning the state," say Blake and Cillizza.

8 pm
The polls close in a whole bunch of states, including Pennsylvania, Michigan, Massachusetts, Connecticut, Maine, Texas, Missouri, much of North Dakota, and Illinois (as well as the rest of Florida and New Hampshire), but not many of them are in play. If Romney wins upsets in Pennsylvania or Michigan, Obama is in trouble. 

But there are several big up-in-the-air Senate races:
Massachusetts: Sen. Scott Brown (R) vs. Elizabeth Warren (D) (Roth: T, Cook: T, Sab: LD, 538: SD)
Connecticut: Rep. Chris Murphy (D) vs. Linda McMahon (R) (Roth: LD, Cook: T, Sab: LD, 538: SD)
Pennsylvania: Sen. Bob Casey (D) vs. Tom Smith (R) (Roth: SD, Cook: T, Sab: LD, 538: SD)
Missouri: Sen. Claire McCaskill (D) vs. Rep. Todd Akin (R) (Roth: SD, Cook: LD, Sab: LD, 538: LD)
North Dakota: Rep. Rick Berg (R) vs. Heidi Heitkamp (D) (Roth: T, Cook: T, Sab: LR, 538: SR)

Among the ballot measures to be decided in this crop of states are proposals to repeal a ban on gay marriage in Maine, legalize gay marriage in Maryland, and approve medical marijuana and doctor-assisted suicide in Massachusetts. 

8:30 pm
votes on whether to be the first state in the South to legalize medical marijuana. 

9 pm
If the races haven't been called in Florida, Ohio, or Virginia, this batch of states becomes more important. At 9 pm, polls close in Colorado, Wisconsin, and Minnesota, as well as safe Obama or Romney states like New York, Arizona, Nebraska, New Mexico, and Wyoming

There are competitive open Senate races in Wisconsin — where former Gov. Tommy Thompson (R) squares off against Rep. Tammy Baldwin (Roth: T, Cook: T, Sab: LD, 538: LD) — and Arizona, where former Surgeon General Richard Carmona (D) is running surprisingly close against Rep. Jeff Flake (R). (Roth: T, Cook: T, Sab: LR, 538: LR

In Colorado, voters will decide if the state will legalize recreational use of marijuana, while Arizona voters will decide on approving medical marijuana. In Minnesota, a constitutional ban on gay marriage is on the ballot.

10 pm
The polls close in the last of the battleground states, Iowa and Nevada, as well as the safe Romney states Montana, Utah, and most of Idaho. Obama is favored to win both Iowa and Nevada. 

Things are much less certain in the last of the closely matched Senate races, in Nevada and Montana. Appointed Sen. Dean Heller (R-Nev.) is hoping to hold off Rep. Shelley Berkley (D) (Roth: T, Cook: T, Sab: LR, 538: LR), while Sen. Jon Tester (D-Mont.) is hoping to fend off a challenge from Rep. Denny Rehberg (R). (Roth: T, Cook: T, Sab: LR, 538: LR)

11 pm
California, Oregon, and Washington finish out the voting in the continental United States. Obama is heavily favored in all three, and there are no competitive Senate races.

Both Oregon and Washington will decide whether to legalize and tax marijuana for recreational use, however, and Washington will also vote on approving gay marriage. Californians will vote on a number of tax measures and could approve a ban on the death penalty. 

Sources: Boston Phoenix, Huffington Post Pollster, GigaOm, New York Daily News, Plain Blog About Politics, Politico, RTT News, The Washington Post