We understand the current crisis of overdose deaths to be driven by widespread opioid use, characterized by distinct ‘waves’ of drug use. The first wave was driven by prescription opioids, the second by heroin, and the third by illicit, non-pharmaceutical fentanyl and fentanyl analogues (henceforth, fentanyl). The purpose of this study is to describe opioid initiation within each of the three waves from the perspective of people who use illicit opioids, with a focus on emerging pathways into fentanyl use. The authors recruited sixty people reporting past-30-day illicit opioid use in Dayton, Ohio. Participants completed a brief survey and a semi-structured in-depth qualitative interview, conducted from March to November 2020 with a total of 13 in-person and 47 virtual interviews. The qualitative interviews were transcribed in their entirety and analyzed thematically using NVivo 12. We noted supply-side changes as influencing trajectories in all three waves. However, we also noted differences in the experiences of prescription opioid and heroin initiation, with these trajectories influenced by pharmacological effects, pain management, curiosity, intergenerational use, pricing, and peers. In comparison, most participants were unaware that they were initiating fentanyl, and many reported overdosing with their first use of fentanyl. We identified a trajectory into fentanyl with limited to no prior heroin use among a few participants. The increased risk of overdose with initiation into fentanyl use further emphasizes the need for an expansion of naloxone distribution and the implementation of more comprehensive measures, such as overdose prevention centers, drug testing, and a safer supply. Further research on the dynamics of the ongoing overdose death crisis in the era of fentanyl and the 4th wave of the overdose crisis is critical in developing responsive prevention and intervention strategies.