Humans and other animals can learn to make different responses as a function of the time between stimuli, as observed in experiments on temporal generalization, duration discrimination, classical conditioning, and temporal preference. They also can learn to adjust the times of their responses as a function of the times of reinforcement, as observed in experiments on the fixed interval reinforcement, the peak procedure, and the differential reinforcement of low response rates procedure. They are also able to track a sequence of intervals, in some cases by using an interval as a discriminative stimulus for the next interval. Although most research on temporal learning has involved a fixed interval between events, their ability to time is not restricted to constant intervals. The initial learning of a temporal interval, and transitions from one interval to another can be rapid. Research on temporal learning has been based on concepts and procedures developed in the study of classical and instrumental conditioning, human and animal psychophysics, and biological rhythms. At present there is no general consensus regarding the relationship between the circadian clock and the various temporal abilities of animals described in this chapter. The same quantitative principles of interval timing apply both to experiments in which time is an attribute of the stimulus and in which it is an attribute of the response. These principles, such as Weber's law for timing, make it possible to develop process models of the process involved in temporal perception and temporal production. Two of the most influential quantitative models of timing are Scalar Timing Theory and the Behavioral Theory of Timing.