From Monday July 18 through Thursday July 21, the Republican Party will be holding their national convention in Cleveland, Ohio. Then, from July 25 to 28, the Democratic Party will hold their convention in Philadelphia, Pennsylvania.

Here are five things you should know about these events:

1. The political party conventions are held every four years as the culminating event of the presidential primary season. For America’s two main political parties, the Democratic Party and the Republican Party, the convention has three main purposes: to officially nominate candidates for president and vice-president, to adopt a party platform, and to decide on each party’s specific rules for internal governance. Although there is no rule governing the timing of the events, the party with the incumbent president tends to hold their convention last.

2. While many different types of people attend the conventions, the official attendees are formally a gathering of “delegates” — political party members chosen as representatives. The delegates (collectively known as the “delegation”) vote on who should be the party’s candidate. The rules adopted by each party during the 2012 conventions established the formulas for determining how many delegates and alternates are allocated to each state during the 2016 election cycle. For example, this year at the Republican National Convention there will be 2,472 delegates and a nominee needs to win receive votes from 1,237 of them — half of the total, plus one — to secure the party’s nomination. Another rule adopted in 2012, known as Rule 40(b), requires that a candidate must have won a majority of delegates in eight states in order to be placed into nomination.

3. Each party has two types of delegates, pledged and unpledged (non-binding). Pledged delegates are representatives of the individual state’s political parties and must cast a vote at the convention for a particular candidate, while unpledged can vote for any candidate. Delegates that are unpledged and not chosen by the primary or caucus system are sometimes referred to by the unofficial moniker of “superdelegates.”

4. In the Democratic Party, current and former Democratic Presidents and Vice Presidents, every Democratic governor (currently, 20 total) and member of Congress (240 total) gets to be a superdelegate, as do former Democratic Majority and Minority Leaders of the U.S. Senate, former Democratic Speakers and Minority Leaders of theU.S. House, and former Chairs of the Democratic National Committee. Altogether the Democrats have 704 superdelegates. This prising about 15 percent of the total delegate count, are a way to provide a check on the popular vote. The GOP has three types of delegates (At-Large Delegates, Congressional District Delegates, and Republican National Committee Members), but unlike the Democrats, these delegates are bound by the same rules as other delegates.

5. During the convention the delegates will also vote on their party’s platform, a document that outlines the statement of principles and policies that the party has decided it will support. Although the document is not binding on the presidential nominee or any other politicians, political scientists have found that over the past 30 years lawmakers in Congress tend to vote in line with their party’s platform: 89 percent of the time for Republicans and 79 percent of the time for Democrats.