In this essay, the relation between computers and their human users will be analyzed from a philosophical point of view. I will argue that there are at least two philosophically interesting relationships between humans and computers: functional and phenomenal relationships. I will first analyze the functional relationship between computers and humans. In doing this, I will abstract from ordinary functions of computers, such as word processor, information provider, and gaming device, to arrive at a generalized account of the functional relationship between humans and computers. Next, I will explore the phenomenal relationship between humans and computers, which is the way in which computers transform our experience of and interaction with our environment or world. Both analyses, I will argue, point to a dual role of computers for humans: a cognitive role, in which the computer functions as a cognitive device that extends or supplements human cognition, and an ambient role, in which the computer functions as a simulation device that simulates objects and environments.