Americans will vote on 8 November to choose their next president.
The candidates are back on the campaign trail since holding their third and final presidential debate on 19 October.
It is a tough task to gauge the mood of a nation that is home to more than 300 million people but that does not stop the pollsters from trying.
National polls tend to have a sample size of about 1,000 people or more and can track movement and general opinion pretty well.
But the US election is won and lost in swing states and decided by the electoral college system.
This means that polls in states that look like they could vote for either candidate (Florida, Ohio and Pennsylvania, to name just a few) play an integral role in election projections.
For Donald Trump to have a chance, he needs to turn Florida and Ohio red and win a few others too.
Trump and Clinton are the only candidates that stand a real chance of winning the race but there are also third-party and independent candidates in the running.
The rules around getting on the ballot differ from state to state but most voters will have two main alternatives to Hillary Clinton and Donald Trump.
Green Party candidate Jill Stein, 66, is a doctor and activist who is hoping to pick up Democrats who backed Bernie Sanders and continue to rally against Mrs Clinton.
Former New Mexico governor Gary Johnson, 63, is standing for the Libertarian Party and focusing his efforts on attracting Republicans uneasy with Mr Trump.
According to Real Clear Politics, Mrs Stein is picking up about 2% of the vote in a four-way race while Mr Johnson is faring slightly better at a little more than 7%. Neither can win the race with stats like that, but they could siphon enough voters off the major candidates to change the outcome in a close race.
Hillary Clinton has long been the frontrunner in this contest but there have been times where she has looked far from comfortable. The most recent examples came back to back in early September.
First, she made headlines by labelling half of Donald Trump’s supporters a “basket of deplorables”, allowing her rival to conclude it was evidence of her disdain for “hardworking people”.
Then just two days later, Mrs Clinton was filmed fainting after leaving a 9/11 memorial service early. It later emerged she had been suffering from pneumonia, fuelling further rumours about her health – rumours that some of her critics have been pushing for months.
Her poll numbers took a noticeable hit in the days that followed but they appeared to recover towards the end of September.
The Republican candidate has made substantial gains on Mrs Clinton since her leads of about 20% in the summer of 2015 (when the field was far wider) but he has only crept ahead of her a few times.
The last came after the Republican National Convention at the end of July when Mr Trump officially accepted the party’s nomination.
The lead did not last long, though, with his rival receiving a similar boost to her ratings at the end of the Democratic National Convention a few days later.
n the past, an astute pick for a candidate’s running mate could earn them a double-digit boost in the polls – Bill Clinton got a 12-point bounce after naming Al Gore as his pick for vice-president in 1992.
But in recent years the bounces have been far smaller, and 2016 followed that trend.
Neither Trump’s choice of Indiana Governor Mike Pence (15 July), or Clinton’s unveiling of ex-Virginian governor Tim Kaine (22 July) changed much in the polls.