Angiogenesis plays a critical role in many normal physiological processes as well as in tumor neovascularization associated with cancer progression. Among various animal model systems designed to study the mechanisms underlying angiogenesis, chick embryo models have been useful tools in analyzing the angiogenic potential of purified factors and intact cells. The chorioallantoic membrane (CAM), a specialized, highly vascularized tissue of the avian embryo, serves as an ideal indicator of the anti- or pro-angiogenic properties of test compounds. In this chapter, we describe a number basic chick embryo CAM models of angiogenesis. A special emphasis is on the model system employing three-dimensional (3D) collagen grafts planted on the CAM, referred herein as onplants. This collagen onplant model allows for unambiguous quantification of angiogenesis and also for in-depth analysis of the cellular and biochemical mechanisms by which specific cells of different origin or purified effector molecules induce or inhibit the angiogenic process.