During the 1990s, biomedical scientists and Muslim religious scholars collaborated to construe Islamic responses for the ethical questions raised by the AIDS pandemic. This is the first of a two-part study examining this collective legal reasoning (ijtihad jamaı). The main thesis is that the role of the biomedical scientists is not limited to presenting scientific information. They engaged in the human rights discourse pertinent to people living with HIV/AIDS, gave an account of the preventive strategy adopted by the World HealthOrganization, and offered an (Islamic) virtue-based preventive model. Finally, these scientists tried to draft a number of Islamic legal rulings (ah. k¯am), usually seen in Islamic jurisprudence as the exclusive business of Muslim religious scholars. This multilayered role played by the scientists reflects intriguing developments in the Islamic religioethical discourse in general and in the field of Islamic jurisprudence in particular.