Although the current interest in informal learning seems recent, performance improvement professionals have long had an interest in informal learning-the ways that people learn outside of formal structures. The earliest forms of learning for work were informal, including de facto and formal apprenticeship programs and the "school of life." Contemporary interest began in the 1960s and 1970s with the rise of self-directed learning. In the 1970s and 1980s, focus shifted to adult learning theory and human performance technology, both of which explore the roles of interventions other than classroom learning. The early 1990s brought two practical applications--electronic performance support systems and edutainment--followed by a third in the late 1990s--knowledge management. Discussions of informal learning arose in the 2000s. Each movement offers practical lessons for designing informal learning today. (Contains 1 table and 1 figure.)