Chile is experiencing a declining electoral participation. In the 1988 plebiscite, 90% of those aged 18 or older voted. In the 2009, only 64% went to the polls. In the 22 years that Chile had a system of voluntary registration and mandatory voting, the decline in electoral participation was not uniform across social groups. In 2010, electoral registration rates among voting age persons in the high income municipalities of Providencia and Las Condes were 97.1% and 69.9% respectively, while in low income municipalities like Maipú and Puente Alto only30.3% and 29% respectively of the voting age population was registered. Starting from the theoretical discussion on the determinants of turnout, we analyze the current debate on electoral participation and the historical evidence on pre 1973 turnout rates and electoral participation after 1989. Using electoral registration data and polls, we analyze the differences between those Chileans registered to vote and those not enfranchised. Until the reform that automatized registration and implemented voluntary voting, the voting population increasingly over represented high income voters. Because decreasing electoral participation can be explained by generational differences in socialization processes, the effects of voluntary voting might end up producing a non-uniform change in electoral participation.