A shield law prevents a court from compelling testimony from a journalist. Twenty-six States provide some statutory protection for reporters' sources, but such laws in California and New Mexico have been found in violation of the separation of powers doctrine. Under this doctrine, no government branch is permitted either to exercise power belonging to another or to interfere with another's administration of its own powers so as to impair its basic function in the constitutional scheme. Whether or not shield laws violate this doctrine hinges on three issues: whether shield laws are primarily substantive or procedural; which branch has ultimate authority over these two spheres; and whether shield laws, even if they are primarily substantive, impair the minimum functional integrity of the courts. Absolute privilege laws, which restrict or abridge the courts' contempt authority, do raise serious questions regarding the separation of powers. Qualified shield laws, which do not impair judicial power and integrity, are less likely to confront a separation-of-powers challenge. 79 footnotes.