Today, Justice Kathryn Werdegar—the current court's longest-serving justice—retires.

Werdegar's retirement, after 23 years on the California Supreme Court bench, gives Gov. Jerry Brown the opportunity to appoint a fourth justice to the seven-member court. Brown appointed Justice Goodwin Liu in 2011, and Justices Mariano-Florentino Cuéllar and Leondra Kruger in 2014.

Here's a primer on how a state Supreme Court appointment is made:

How to Become a Supreme Court Justice

For more information about how justices are selected, go to http://www.courts.ca.gov/3162.htm.