Although individual learning has elicited substantial theoretical and empirical attention for well over 100 years, systematic work on how groups and organizations learn from their experience, retain the knowledge they acquire, and transfer this knowledge is much more recent. Moreover, because the literatures on group and organizational learning developed relatively independently, few efforts have been made to analyze their similarities and differences. The goals of this Handbook are to provide comprehensive and up-to-date reviews of both fields by leading scholars, to identify important cross-cutting themes, and to suggest productive avenues for future research. Contributions are organized under two major headings -- (1) processes of group and organizational learning and (2) contextual influences on group and organizational learning. The former includes chapters on mindfulness of learning processes, information sampling and search, information processing and interpretation, training, remembering and retaining knowledge, performance feedback and social comparisons, learning from others and transferring knowledge, and innovation and creating knowledge. The latter includes chapters on unit composition, structures and routines, intergroup contexts, and online environments. An integrative chapter identifies connections between the chapters and also points out directions for future research.