From his first book, The Nature of Managerial Work, to his latest, Mintzberg on Management, Henry Mintzberg has been a provocative, influential voice in the general management discussion. This article develops his work on organizational structures, refining his theories to better explain how effective organizations manage the contradictory internal forces that can so easily tear them apart. There is no best way, he argues; organizations must build their own structures, using established forms or combining them. But while there is no blueprint for the effective organization, we can be aware of the dangers — when the force for efficiency, for instance, begins to suppress innovation, or when healthy internal competition deteriorates into petty politics. Managing an organization is like building with LEGOs, he writes, and the best structure is the one that balances forces most gracefully.