Halotools is a specialized python package for building and testing models of the galaxy-halo connection, and analyzing catalogs of dark matter halos. The core functionality of the package includes: Fast generation of synthetic galaxy populations using HODs, abundance matching, and related methods; Efficient algorithms for calculating galaxy clustering, lensing, z-space distortions, and other astronomical statistics; A modular, object- oriented framework for designing your own galaxy evolution model; End-to- end support for reducing halo catalogs and caching them as fast-loading hdf5 files