Category Theory is one of the most abstract branches of mathematics. It is usually taught to graduate students after they have mastered several other branches of mathematics, like algebra, topology, and group theory. It might therefore come as a shock that the basic concepts of category theory can be explained in relatively simple terms to anybody with some experience in programming. That's because, just like programming, category theory is about structure. Mathematicians discover structure in mathematical theories, programmers discover structure in computer programs. Well structured programs are easier to understand and maintain, and are less likely to contain bugs. Category theory provides the language to talk about structure, and learning it will make you a better programmer.