It is well known that irrelevant stimuli can control where we attend. However, in the literature about the so-called attentional capture phenomenon, there has been a great deal of discussion about the extent to which such effects are automatic or rather modulated by endogenous factors. The present article reviews data and theory related to this debate. Although both exogenous and endogenous factors appear to have an influence on attentional allocation, mental sets related to the task at hand seem to be the most influential in modulating attentional capture. As such, although attentional capture appears to be automatic “by default”, in that it can occur in the absence of a specific mental set, it seems clear that it can be endogenously modulated.