This year sees the anniversary of Donald O. Hebb's birth, in July 1904. The impact of his work, especially through his neurophysiological postulate, as described in his magnum opus, The organization of behaviour (1949), has been profound in contemporary neuroscience. Hebb's life, and the scientific milieu in psychology and neurophysiology which preceded and informed Hebb's work are described. His core postulate, which gave rise to such eponymous expressions as the Hebbian synapse and the Hebbian learning rule, is examined in some detail, as well as the part it played in his higher-order theoretical constructs concerned with neocortical structure and function. Early models which made use of the Hebbian synapse are described, and then illustrative examples are given detailing the impact of Hebb's idea in relation to learning and memory, synaptic plasticity and stability, and the question of persistent cortical activity underlying forms of short-term memory.