At present, there does not appear to be a satisfactory theory of the sequential organization of behaviour. A number of experiments on tachistoscopic recognition and dichotic listening, in which it is necessary to respond sequentially to simultaneously presented stimuli, are reviewed. The data from these experiments indicate that the order of responses is determined by the spatio-temporal arrangement of die stimulus elements, by the experimental set, and by learned associations between the individual elements. On the basis of these data, a model for serial order is developed and applied to other situations with some success.IN GENERAL, PSYCHOLOGICAL THEORY and experimentation have been concerned with the relation between simple stimulus events and responses. Typically, however, a response to a stimulus is not an isolated bit of behaviour, but rather a single incident in a long series of responses. In speech or piano playing, for example, the important behaviour is not the single response, but the response in its temporal relation to other responses. It is clear that a complex temporal integration of neuronal activity must underlie such behaviour. To date, few attempts have been made to work out the basis of serially ordered behaviour, perhaps because of the complexity of the behaviour involved and the difficulty of analysing it experimentally.The most systematically developed theories of the temporal integration of behaviour are the associative chain theories. Perhaps the best statement of this position has been made by Hull (1930), although essentially similar ideas have been proposed by Bechterev (1932), Washburn (1916), and Watson (1924, among others. More contemporary versions of the associative chain theory have been presented by Berlyne (1965) and 1 The preparation of this paper was facilitated by grants to the author from die National Research Council of Canada (APA-95) and the Defence Research Board of Canada (9401-26), and by D.R.B. Grant No. 9401-11 to D. O. Hebb. I am indebted to Professors Woodburn Heron of McMaster University, D. O. Hebb of McGill University, and R. V. Thysell of the University of Waterloo for their stimulating and critical discussion of an earlier draft of this paper, and to many of my colleagues and students at the University of Waterloo for their comments on the 2