Under Approval Voting, voters can ''approve" as many candidates as they want, and the candidate approved by the largest number of voters is elected. Since the publication of the seminal book written by Steven Brams and Peter Fishburn in 1983, a variety of theoretical and empirical works have enhanced our understanding of this method. The behavior of voters in such elections has been observed both in the laboratory and in the field; social choice theorists have analyzed the method from the axiomatic point of view; game theory and computer science have been used to scrutinize various strategic aspects; and political scientists have considered the structure of electoral competition entailed by Approval Voting. This book surveys this large body of knowledge through a collection of contributions written by specialists of the various disciplines involved.