This chapter presents a review of selective attention functioning in Alzheimer's disease (AD). The primary focus is on work conducted into this complex topic within the author and colleagues' laboratories (i.e. studies of simple and conjoined visual search). Findings obtained by the author and colleagues investigating simple and conjoined feature visual search in AD are related to findings obtained in the same laboratories in the healthy elderly and in patients with Parkinson's disease. Selective attention is a complex, multifactorial entity. Impairment of selective attention may be an early feature of AD and a prominent clinical characteristic of some patients. However, there are currently few reliable clinical measures of attentional dysfunction in AD. The experimental literature implicates some aspects of selective attention more reliably in AD than others. With respect to our own empirical studies, more effortful or controlled aspects of selective attention (as characterized by conjoined feature visual search) are impaired in AD. Furthermore, on the basis of our experimental observations, these aspects of selective attention appear to be disproportionately impaired relative to deficits in other cognitive domains that have previously been reported in the AD literature. By contrast, conjoined feature visual search deficits were not observed in our studies in patients with Parkinson's disease. The selective attention deficits that we have noted in AD patients represent an extension of the types of impairments that we have also observed in healthy aging; that is, compared with the healthy elderly, AD patients were quantitatively but not qualitatively more impaired on conjoined feature visual search. This is an important observation. The ways in which these findings relate to the wider AD selective attention literature are also considered, drawing out several common theoretical strands across a range of empirical studies.