Everything You Need to Know About a Contested Convention

The Republican presidential election could be headed to a contested convention—that’s when there’s no clear nominee going into the party’s July convention in Cleveland.

If no one candidate wins the support of 1,237 delegates by the time the convention starts on July 18, the nomination could be up for grabs. It will be up to the delegates themselves to choose whether to nominate front-runner Donald Trump, his rivals Ted Cruz or John Kasich, or even another candidate. But if Trump manages to win Tuesday’s Indiana primary, the odds of a contested convention will be significantly smaller.

In the video above, TIME explains exactly how a contested convention works and how it could create yet another surprise in the rocky Republican race.