In this review, we aim to bring together major trends in autism research at three levels: biology, behaviour and cognition. We propose that cognitive theories are vital in neuropsychology, which seeks to make connections between brain abnormality and behavioural symptoms. Research at each of the three levels is incomplete, but important advances have been made. At the biological level, there is strong evidence for genetic factors, although the mechanism is, as yet, unknown. At the behavioural level, diagnosis and education are becoming more coherent and less controversial, although the possibility of autism subtypes has provoked new debate. At the cognitive level, three major theories are proving fruitful (mentalizing impairment, executive dysfunction and weak central coherence), although the relation and overlap between these is uncertain. Rapidly advancing technology and methodology (e.g. brain imaging, gene mapping), as tools of cognitive theory, may help to make autism one of the first developmental disorders to be understood at the neuropsychological level.