The starting point of our work is that skilled, seemingly automatic, performance of tasks such as word and object identification is flexible and can be powerfully influenced by contextual factors that include memory and conceptual knowledge. We describe three situations in which various forms of stimulus selection during task switching are influenced by the processing operations or knowledge bases configured in advance to complete a task. The first situation we consider involves the nature of the interaction between a response to an unambiguous stimulus (task 1--read a word printed in black) and the requirement to avoid making a similar response to an upcoming ambiguous stimulus (task 2--name the color in which a word is printed). Results show that responding in task 1 is substantially slowed when it is predictably followed by task 2. Our evidence indicates that this effect has a component that is specific to phonological processes involved in word reading, suggesting that phonological encoding of words is subject to strategic, though not necessarily conscious, modulation. The next kind of interaction we consider involves selection from an ambiguous event in memory (a color Stroop stimulus). In this situation, where selection takes place from a stimulus event that is no longer directly perceived (i.e., the stimulus has been encoded into immediate memory), our results indicate a robust reverse Stroop effect that sometimes is as large as the basic Stroop effect, even though standard color-word Stroop tasks typically reveal little or no reverse Stroop effect. Finally, we examine the nature of the interaction between selection in immediate memory and conceptual knowledge recruited when identifying objects. We discuss the important consequences of this kind of interaction for theoretical accounts of the effect of semantic category on normal and neurologically impaired object identification.