Since the passage of the “Help America Vote Act” in 2002, nearly half of the states have adopted a variety of new identification requirements for voter registration and participation by the 2006 general election. There has been little analysis of whether these requirements reduce voter participation, especially among certain classes of voters. In this paper we document the effect of voter identification requirements on registered voters as they were imposed in states in the 2000 and 2004 presidential elections, and in the 2002 and 2006 midterm elections.