Tumor angiogenesis, the formation of new blood vessels from existing vasculature in response to chemical signals from a tumor, is a crucial step in cancer invasion and metastasis. Though the detailed processes involved in angiogenesis are well established, the biomechanical and biochemical mechanisms behind the vessel formation are largely unresolved. We have developed a cell-based, multiscale modeling framework that has been successfully applied to study tumor induced angiogenesis. Our multiscale model is the first to incorporate intracellular signaling pathways, cellular dynamics, cell-cell, cell-matrix, cell-environment interactions, as well as chemical dynamics, for tumor-induced angiogenesis. It is also the first to simulate emergent vessel branching, anastomosis, and the brush border effect. I will show that the model has not only reproduced realistic sprout morphogenesis, but also generated testable hypotheses regarding mechanistic role of angiogenic factor (VEGF) and the topography of extracellular matrix, on sprout branching and fusion.