Abstract
Federal and state legislative elections rely heavily on geographic electoral districts, which makes the districting map itself an important component of the electoral system. This chapter situates contemporary electoral mapmaking in historical and institutional context, tracing how redistricting evolved from the geographic approach of early state legislatures in the direction of increasing federal constraint, judicial intervention, and attention to nongeographic representational considerations. The U.S. Supreme Court has construed federal constitutional and statutory law to mandate approximate population equality and to regulate the role that race, but not politics, plays in the drawing of district lines. Federal redistricting law imposes important constraints on state mapmakers, but still leaves them plenty of discretion. States channel this discretion through a wide variety of state redistricting criteria designed to further constrain and guide mapmakers as they navigate the trade-offs between conflicting representational values.