For a first introduction to category theory, from the masters thereof, I would highly recommend the book by Lawvere and Shanual "Conceptual Mathematics: A First

For a first introduction to category theory, from the masters thereof, I would highly recommend the book by Lawvere and Shanual "Conceptual Mathematics: A First Introduction to Categories". It almost doesn't look like a mathematics book, but believe me, these guys know what they are talking about. They distill some very high-brow ideas down to something us mere mortals can grok.