Reinforcement is a naturally occurring behavioural condition that was experimentally demonstrated in the labs of B. F. Skinner in 1938 and has served as the basis for the field of applied behavioural analysis. The basic two-term contingency of response–consequence can be expanded upon and has multiple applications, including detailed schedules of reinforcement, differential reinforcement, as well as negative reinforcement. There are also a number of factors that influence the effectiveness of the implementation of reinforcement as a behavioural application, including identifying the behaviour to be reinforced, choosing appropriate reinforcers, the use of motivating operations, the immediacy of reinforcers, and making reinforcers contingent. Finally, some of the controversy surrounding the use of reinforcement in the classroom will be reviewed.