The obligation to help others often involves personal risk. Consequently, the scope and boundaries of this obligation can present a complex dilemma, which has practical and moral implications, even in the world of medicine. In Jewish medical ethics, the dilemma stems from a confrontation between the duty to help others according to the biblical commandment: "Do not stand idly by your fellow's blood" on the one hand, and between the right and duty of man to defend himself, which is anchored in Jewish law. This article surveys the sources of this quandary in Jewish texts throughout the ages such as the Bible, Mishnah, Talmud, and responsa literature in various contexts. The discussion highlights the essential difference between the formal demands of the law, which protects human rights of self-preservation, and the moral requirement to help others even if it may include personal risk. The sources suggest distinguishing between various levels of risk ranging from high-risk to reasonable or low risk. In this way, the classic sources, provide the foundation and the tools for grappling with modern contemporary Halachic questions such as organ transplantation, and generate a Torah value-based framework to deal with new situations that may arise in the future. It is critical to assess the level of risk and the chances for success, along with other subjective considerations, in order to ensure the optimal ethical course of action.