With the pioneering work of Weeks (1961,1962) and others (Thompson and Schuster, 1964 ; Collins and Weeks, 1965 ; Deneau et al., 1969 ; Yanagita and Takahashi, 1973 ), which showed that laboratory animals would voluntarily ingest psychoactive drugs, an enormous field of research has developed that uses “self-administration” techniques to study drug reinforcement. This chapter deals with some of the methods employed in self-administration studies involving rats, with special emphasis placed on the schedules of reinforcement that govern drug delivery.