Previous research has established the importance of early interest in STEM as a key factor in persistence. Our current research builds on this foundation and extends it to add more detail to understanding the types of experiences that trigger and maintain interest in science, technology, engineering, and mathematics (STEM). Using survey data from nearly 8,000 individuals, we are able to address the "When?," "What?," and "Who?" of those first experiences. Additionally, our data provide information on the types of experiences that maintained interest (or not) beyond the triggering event. Through purposeful sampling, our data include those who ended up in STEM fields and those who did not, which allows us to make important comparisons across these groups. Overall, our findings indicate that individuals who complete STEM degrees have quite varied histories and that the triggering of their interest happened across a wide age spectrum. Similarly, in terms of who was involved or what their triggering experience was, the general results support the notion that there are many pathways to STEM with no clear preferential pathway.