Large public sector organizations—government agencies, multilateral institutions, and non-profits—today face unprecedented management challenges, including entrenched organizational structures, complex stakeholder environments, and shifting regulatory regimes. Problems which result from these challenges have come to define the very meaning of the word “bureaucracy”: slow decision-making, high costs, and resistance to change. There are many reasons why reaching high performance is difficult for any organization, and additional factors make it even harder in the more-constrained, more-transparent public sector. This Monitor Group paper, based on their practical experience with clients in all types of organizations and a recent research effort looking specifically at large bureaucracies, sheds light on the drivers of and barriers to high performance and derives a set of actionable improvement imperatives without which significant change cannot occur.