The planning of organic syntheses, a critical problem in chemistry, can be directly modeled as resource- constrained branching plans in a discrete, fully-observable state space. Despite this clear relationship, the full artillery of artificial intelligence has not been brought to bear on this problem due to its inherent complexity and multidisciplinary challenges. In this thesis, I describe a mapping between organic synthesis and heuristic search and build a planner that can solve such problems automatically at the undergraduate level. Along the way, I show the need for powerful heuristic search algorithms and build large databases of synthetic information, which I use to derive a qualitatively new kind of heuristic guidance.