 Sustainable, integrated PrEP adherence interventions are critically needed to reduce HIV incidence among YMSM and YTW. It is imperative that the investigators develop adherence interventions for YMSM and YTW initiating PrEP that are engaging, age-appropriate and take advantage of technologies that are already embedded in these individuals lives. A smartphone-delivered PrEP adherence intervention is well suited for this population, given they have a high-uptake and utilization of smartphone technology. The use of smartphones to deliver HIV prevention and care interventions has grown substantially in recent years due to: a wide-scale adoption of smartphone technology among high-risk groups, b the ability to deliver interventions in real-time within risk contexts, and c low implementation costs.The accessibility, affordability, anonymity and acceptability of smartphones make them the intervention medium of choice for engaging youth and a logical platform to deliver an adherence intervention targeting PrEP. Further, smartphone interventions address can overcome issues that impede engagement with in-person interventions such as transportation logistics, stigma and confidentiality. Further youth, including YMSM and YTW are receptive to smartphone delivered interventions and these interventions can impact HIV related prevention behaviors. 