Atom probe tomography (APT) is a destructive material characterization technique that can analyze the composition of small volumes (~100×100×100 nm3) of a sample with subnanometer resolution and part per million sensitivity. APT is therefore well suited to investigate semiconductor nanostructures in order to relate growth conditions to nanoscale structure and nanostructure to physical properties. Furthermore, the geometry of semiconductor nanowires facilitates their analysis by APT. This chapter is intended for scientists and engineers who are interested in using APT to characterize semiconductor nanowires or for those who wish to assess research findings derived from APT more critically and with a greater understanding of the method. We first introduce the principles of APT to provide the basic background needed to understand the capabilities and limitations of the method, and then briefly review experimental considerations including sample preparation, operation conditions, and reconstruction guidelines. We then present examples of the atom probe analysis of semiconductor nanowires focused on important analytical challenges including dopants and impurities, alloy fluctuations and clusters, and heterointerfaces. Concurrently, we explain key challenges to sample preparation and analysis and suggest approaches to overcome or circumvent these challenges.