Angiogenesis, or the process of new blood vessel formation, is a natural event that occurs under both normal and pathological conditions. In the normal state, two distinct processes can be seen. One process utilizes endothelial progenitor cells. These are usually derived from bone marrow and initiate endothelial growth and vascular tube formation. The second process utilizes existing vasculature to generate new vessels, and is highly dependent on endothelial cell activation and protease secretion. Under pathological conditions, many of the same steps involved in normal vessel formation are repeated. However, the structures formed are often functionally abnormal, possibly due to an imbalance in the angiogenic process. Multiple factors contribute to angiogenesis, including soluble growth and differentiative factors, extracellular matrix components, membrane-bound receptors, and intracellular signaling molecules. R&D Systems has an extensive and diverse offering of reagents for studying proteins that are known to be involved in both angiogenesis and its natural counterpart, anti-angiogenesis.