In this talk, I will focus on recent efforts to study solid tumor progression. Here we focus on a continuum-scale description and pose the problem in terms of conservation laws for nutrients, chemical factors and tumor cell populations. We focus first on single-phase models. We analyze the equations and develop accurate, adaptive numerical schemes. We will present simulations of the complex nonlinear coupling between the progression of the tumor and neovascularization. We demonstrate the predictive capability of the model through comparisons with in vitro and in vivo experimental studies of tumor growth. We then discuss extensions to multiphase and mixture models and discuss the effects of residual stress and cell-to-cell adhesion.