Angiogenesis is a term that describes the formation of new capillaries from a pre-existing vasculature. This process is very important in physiologic conditions because it helps healing injured tissues, and in female populations it helps forming the placenta after fertilization and reconstructs the inside layer of the uterus after menstruation. Angiogenesis is the result of an intricate balance between proangiogenic and antiangiogenic factors and is now very well recognized as a powerful control point in tumor development. In this particular environment, the fine modulation among proangiogenic and antiangiogenic factors is disrupted, leading to inappropriate vessels growth. In this review, we discuss the molecular basis of angiogenesis during tumor growth and we also illustrate some of the molecules that are involved in this angiogenic switch.