This article analyses the nature of learning in three long-term professional development approaches from different disciplines--teacher research as used in educational contexts, action learning as used in business contexts, and problem-based learning as used in medical contexts. The lens used for analysis focuses on three dimensions or influences on learning--the action setting, personal influences and sociocultural influences. Although the dimensions are present in each approach, they have a different emphasis. It is argued that planning for long-term professional development needs to consider all three dimensions in conjunction because the key for sustainability in professional development is the dynamic interplay between the dimensions. (Contains 2 tables, 1 figure and 1 note.)