Theories of associative learning are concerned with the factors that govern association formation when two stimuli are presented together. In this article we review the relative merits of the currently influential theories of associative learning. Some theories focus on the role of attention in association formation, but differ in the rules they propose for determining whether or not attention is paid to a stimulus. Other theories focus on the nature of the association that is formed, but differ as to whether this association is regarded as elemental, configural, or hierarchical. Recent developments involve modifications to existing theories in order to account for associative learning between two stimuli, A and B, when A is accompanied, not by B, but by a stimulus that has been paired with B. The implications of the theories for understanding how humans derive causal judgments and solve categorization problems is considered.