Angiogenesis, or new blood vessel growth, is essential for the growth, invasion, and metastasis of solid tumors. The inhibition of this process, or antiangiogenesis, is a promising new therapeutic anticancer strategy. Several antiangiogenic compounds are currently in preclinical or clinical development for the treatment of cancer. However, the challenge for the discovery and characterization of antiangiogenic targets remains in developing efficient in vitro or in vivo preclinical angiogenesis screening assays to assess and compare antiangiogenic activity. Several semiquantitative or quantitative angiogenesis assays exist, including in vitro endothelial cell systems and ex vivo or in vivo neovascularization models utilizing mouse, rat, or human tissues. We describe the more common and cost-effective angiogenesis assays currently in use, summarizing their unique advantages and disadvantages. Since angiogenesis inhibition is a novel therapeutic modality towards controlling solid tumors, antiangiogenic drug development underlines the importance in describing, standardizing, and developing quantitative screening assays for the next generation of antiangiogenic agents. This is a US government work. There are no restrictions on its use.