The history of computing education research is replete with studies about learning in formal contexts (i.e., students learning from teachers in school classrooms). In this chapter, we explore other contexts in which learning about computing occurs (e.g., through reading books, working through online tutorials, competing in hackathons, or asking and answering computing questions on a Q&A website). These activities are all examples of informal learning – learning that is opportunistic, rather than planned; unstructured, rather than pedagogically created; self-directed, rather than teacher-centric; and integrated authentically into life activities (Marsick & Watkins, 2001), rather than taking place in a classroom environment. We collect and synthesize research about informal learning of computing and discuss open questions around where and how it occurs and how to best support it.