In spite of attitudes that range from caution to prohibition regarding music, the worlds of Islam are rich with musical genres and performance practices, from liturgical chant to internationally-renowned musics like Pakistani qawwali or the music and dance of the Turkish Mevlevi, the famous Whirling Dervishes. Indonesia (often cited as the country with the largest Muslim population in the world) alone hosts a remarkable variety of Islamic music and the enthusiastic acknowledgment of and participation in Islamic music among a broad cross section of the population puts this Muslim member of the Islamicate world in a class of its own. From the sublime to the ridiculous, seni musik Islam, whether rooted historically in Arabic or local Indonesian styles, or created anew from the fabric of international pop, is considered meritorious because of its unquestionable quality of dakwah (strengthening or bringing more people to the faith). From seashore to department store, Islamic music is performed and experienced, produced and purchased in an array of overlapping categories, interdependent processes, and reciprocal influence that eschews clean boundaries or unidirectional cause and effect. Nevertheless the musics of Indonesian Islam distinctly reflect and generate the social and political communities and ideologies that characterize contemporary Islam in Indonesia. In presenting an array of Islamic musics – from the music melayu that rings with the lilt of the Indian sub-continent, to the lively interlocking patterns of rebana and hajir-marawis, indebted to the gulf, to the revered Arabic texts rendered in Egyptian maqam, to the international pop sounds of nasyid, and the myriad species of musics from the grass-roots -- I suggest ways in which we can interpret Indonesian Islam with particular regard to the intersection of two of the most supposedly controversial aspects of Islamic performance, the public participation of women, and the use of musical instruments. While the presentation is based on extensive research in Indonesia, I hope to benefit enormously from the observations and expertise of colleagues interested in the ways music moves religion throughout the cultural worlds surrounding the Indian Ocean.