The invention provides Cripto blocking antibodies, or biologically functional fragments thereof, and uses thereof. Antibodies which bind Cripto and modulate Cripto signaling are provided. Antibodies which bind Cripto and block the interaction between Cripto and ALK4 are provided. Antibodies which bind Cripto and modulate tumor growth are also provided. Antibodies which bind Cripto, modulate signaling, and modulate tumor growth are also provided. Antibodies which bind Cripto, block the interaction between Cripto and ALK4 and modulate tumor growth are provided. The invention also provides methods of using these antibodies in therapeutic, diagnostic, and research applications.