Early voting is starting in some states. Less than 50 days remain before Election Day, and registration deadlines are fast approaching for several states. It’s crucial for potential voters to ensure they are eligible to vote and registered to do so.

Here’s what you need to know:

How to check your existing voter registration or register to vote in general

Each state operates a website where residents can check their voter registration status; many provide online registration, and all provide information on how to register. NPR’s How to Register to Vote website includes links to the voter registration sites for each U.S. state and territory.

Even if you believe you are registered or have voted in past elections, you should still check your registration. Certain states or localities remove voters who have not voted in one or more previous elections from active voter rolls. Additionally, voters who have changed addresses may need to register again at their new location to be eligible to vote. As states purge their voter rolls of ineligible voters — a process that has been accused of being done in a heavy-handed, partisan and biased manner in some states — some eligible voters may have been removed; these voters will need to clear up these mistakes to confirm they can vote.

How to your voter eligibility

The website USA.gov, which also links to each state’s voter registration pages, notes that to be eligible to vote, U.S. citizens must be at least 18 years old by Election Day. Voters must also meet the state’s residency requirements in which they plan to vote.  In addition to these requirements, some states ban or restrict voting for people who are incarcerated or have a past felony conviction, and some also restrict voting for people with mental disabilities.

The votes to determine the next president, control of Congress and a variety of other offices are all expected to be close this election. Every vote will, therefore, count, making it more critical that everyone who wants to vote makes sure that they will be able to do so.