This project will measure, model, and interpret the clustering of galaxies on scales of 10 kiloparsecs to 1 megaparsec -- small scales in the cosmological context. The project consists of four main science goals. (1) Constrain the spatial distribution of galaxies inside dark matter halos in the local universe. Using redshift data from the Sloan Digital Sky Survey (SDSS), the proposing team will measure the projected two-point correlation function, the angular correlation function, and the surface density profile of galaxies in groups and clusters. They will model these statistics to constrain the density profile of galaxies in dark halos, using both analytic models and numerical models constructed from cosmological N-body simulations. (2) Extend the above analysis to higher redshift by using data from the new Baryon Oscillation Spectroscopic Survey (BOSS). Modeling the correlation functions will reveal the recent evolution in the spatial distribution of galaxies within halos. (3) Refine the proposers' semi-analytic model for the evolution of dark matter subhalos under the influence of merging, improving the analytic prescription for mass loss and including the role of baryonic matter. (4) By comparing the improved halo model to the clustering statistics, constrain the star formation and star stripping efficiencies for galaxies merging with larger halos. The project will support the work of several graduate and undergraduate students at the two collaborating institutions. In addition, the project will provide funding for summer K-12 science camps so that minority students in the Nashville, TN area will be able to attend without financial burden.