Due to Major League Soccer being a salary cap league, there are many roster mechanisms that are unlike those usually seen in the global game of soccer, from needing to use General Allocation Money to purchase players and buy down salaries to having a draft for players coming out of college. Mechanisms like this are standard to American sports fans as every league has quirks that come with it, but due to the global reach of MLS and its place in the global soccer market, more people are beginning to learn about these quirks by the day.

One that has come up quite a lot since players like Marco Reus and Lionel Messi came to the league is Discovery Rights and the Discovery List.

So what do they mean?

This has existed since the league was formed in 1996 and allows a team to list up to five players who are not under contract with MLS or attached to another assignment mechanism. These players can't be current MLS players, players who have played in MLS previously, draft-eligible or homegrown-eligible players, or free agents, along with a few other stipulations. A team can add or remove anyone from their list at any time, and there is no limit to how many players who can be signed via this mechanism.