Associationism can be broadly defined as a school of thought in philosophy and psychology that holds that mental activity can be accounted for by processes that combine simple elements or ideas. More than a century ago, scientific psychology started taking measurements of word associations, and only a few years later, word associations became a major research tool in psychiatry. With the advent of neurobiology and the discovery of the neuron, the term association came to denote physical connections between cells or parts of the brain. The resulting ambiguity made the concept highly fruitful and at the same time introduced the risk of committing categorical mistakes and of engaging in unfounded speculation, since little was known about the actual functioning of neurons. In modern cognitive neuroscience, computational models provide the critically needed link between the psychological and the biological approaches. The concept of association, with its biological, psychological, and computational connotations, provides the framework needed for further experimental research. Its potential for contributing to our understanding of psychopathology can hardly be overestimated.