This dissertation defends extended cognitivism: a recently emerging view in the philosophy of mind and cognitive science that claims that an individual's cognitive processes or states sometimes extend beyond the boundaries of their brain or their skin to include states and processes in the world. I begin the defence of this thesis through a background discussion of several foundational issues in cognitive science: the general character of cognitive behaviour and cognitive processes, as well as the nature and role of representation (...) as it is standardly taken to figure in cognition. I argue in favour of the widely held view that cognition is best characterised as involving information processing, and that carriers of information are ineliminable components of the most distinctively human and powerful forms of cognition. Against this background the dissertation argues in stages for successively stronger claims regarding the explanatory role of the external world in cognition. First to be defended is the claim that cognition is often embedded in one's environment. I develop this claim in terms of what I call 'parainformation': roughly, information that shapes how we tackle a cognitive task by enabling the extraction of task-relevant information. Proceeding then to the defence of extended cognitivism, I draw most significantly on the work of Andy Clark. In outline, and in general following Clark, it is argued that states and processes occurring beyond the skin of the cognitive agent sometimes play the same explanatory role as internal processes that unquestionably count as cognitive. I develop this claim in two versions of differing strength: firstly, in a general way without commitment to the representational character of extended cognition, and secondly in a specifically representational version with special attention to intentional explanation. Against each of these versions of extended cognitivism are ranged a number of criticisms and objections, many of which stem from the work of Fred Adams and Ken Aizawa. The dissertation examines these objections and rejects each of them in turn. (shrink)