This chapter provides an overview of molecular mechanisms that guide axon extension during neural development. It introduces the growth cone, a specialized motile structure at the tip of the axon responsible for sensing and responding to guidance cues. Growth cone morphology is a direct consequence of the organization of the two main components of its cytoskeleton, microtubules, and filamentous actin. The chapter describes the trajectory of embryonic spinal commissural axons, and reviews axonal guidance cues. It presents a description of the growing understanding of the cellular and molecular mechanisms that transduce extracellular guidance cues into directed axon growth. As an axon extends along its trajectory, its growth cone has the capacity to change its response to local guidance cues. The chapter concludes with a discussion on the possibility that cues now known to regulate axon guidance during development may subsequently influence axon regeneration in the adult central nervous system (CNS).