The BlueD Study will involve conducting a literature review and developing mathematical models to explore different scenarios of providing a combination HIV prevention service intervention for MSM in China. Using information from this exercise, we will develop and pilot test a combination HIV intervention built into a smartphone app. The intervention will include home care services such as home HIV self-testing and home ordering of prevention products such as condoms. The intervention will be built into the existing BlueD platform, which is the largest geosocial networking app used by MSM in the world.