Both in research and practice, many believe that informal work-related learning contributes to plenty of important and positive outcomes. As a result, research on informal work-related learning outcomes is quickly accelerating. The field has become fragmented across disciplines and traditions. In response, this study provides a systematic review of the literature on outcomes associated with informal work-related learning behaviour of employees. In total, 39 studies were included in our review. Our results show that outcomes associated with informal work-related learning behaviour go beyond the specific job, as is sometimes assumed. Instead, outcomes vary across dimensions, going from hands-on to abstract, short-term to long-term, or job-specific to more generic. We provide an overview of outcomes in three categories, namely (1) changes in knowledge, skills, and attitudes, (2) individuals' and organizations' professional achievement, and (3) sustaining a future development.