HIV testing and service uptake are infrequent among people who use drugs (PWUD) in the United States. In partnership with a community-based syringe service program (SSP), this project will develop the SSP-based "Prevention Ambassadors" (PA) intervention to promote HIV testing and service uptake among PWUD via the secondary distribution (i.e., peer delivery) of HIV self-testing (HIVST) kits with local HIV service information and referrals to HIV service navigation in the social networks of SSP clients (i.e., PWUD). The PA intervention will then be piloted to assess its preliminary effects, acceptability, and feasibility among PWUD in the Ending the HIV Epidemic priority jurisdiction of Riverside County, California.

Index Participant Inclusion Criteria:

• Being greater than or equal to 18 years old
• Reporting drug use (past month)
• Having other people who use drugs (PWUD) in one's social network
• Being willing to talk about HIV testing and services with at least 2 PWUD in their networks and attempt to refer them to the study
• Speaking English fluently

Peer-Recruit Participant Inclusion Criteria:

• Being greater than or equal to 18 years old
• Reporting drug use (past 3 months)
• Being recruited by an index participant (evidenced by presenting the coupon used to recruit them)
• Speaking English fluently

Exclusion Criteria:

- Persons who participated in formative study activities related to the development of the PA intervention will not be eligible to participate.

De-identified data will be made available upon review of written requests from researchers.

Approximately 6 months after the publication of the study's primary findings.

Requests from researchers for de-identified data will be reviewed by the research team (Multiple Principal Investigators and Co-Investigators).