The purpose of this formative research, guided by the Integrated Behavioral Model, was to assess men's attitudes and personal agency towards HIV self-testing (HIVST) and confirmatory HIV testing in order to inform the development of the Tanzania STEP (Self-Testing Education and Promotion) Project, a peer-based HIV self-testing intervention for young men in Tanzania. Qualitative in-depth interviews were conducted with 23 men in Dar es Salaam, Tanzania who socialize in networks locally referred to as "camps". Men reported privacy, confidentiality, and saving time as the primary reasons for their self-testing interest. Most participants had high perceived control and self-efficacy to self-test and seek confirmatory HIV testing. Nevertheless, men reported concerns related to their ability to perform the test and the potential lack of post-test counseling. Specific recommendations for the intervention included providing HIVST education and pre-test counseling, and using mobile health (mHealth) strategies for participants to reach a healthcare professional for further assistance. The findings suggest that while HIVST is highly acceptable among men in Tanzania, future interventions will need to address the challenges that men may face with HIVST before promoting it as an alternative or supplement to facility-based HIV testing.