In more than 30 essays for Harvard Business Review, Peter Drucker (1909-2005) urged readers to take on the hard work of thinking--always combined, he insisted, with decisive action. He closely analyzed the phenomenon of knowledge work--the growing call for employees who use their minds rather than their hands--and explained how it challenged the conventional wisdom about the way organizations should be run. He was intrigued by employees who knew more about certain subjects than their bosses or colleagues but who still had to cooperate with others in a large organization. As the business world matured in the second half of the twentieth century, executives came to think that they knew how to run companies--and Drucker took it upon himself to poke holes in their assumptions, lest organizations become stale. But he did so sympathetically, operating from the premise that his readers were intelligent, hardworking people of goodwill. Well suited to HBR's format of practical, idea-based essays for executives, his clear-eyed, humanistic writing enriched the magazine time and again. This article is a compilation of the savviest management advice Drucker offered HBR readers over the years--in short, his greatest hits. It revisits the following insightful, influential contributions: "The Theory of the Business" (September-October 1994), "Managing for Business Effectiveness" (May-June 1963), "What Business Can Learn from Nonprofits" (July-August 1989), "The New Society of Organizations" (September-October 1992), "The Information Executives Truly Need" (January-February 1995), "Managing Oneself" (March-April 1999 republished January 2005), "They're Not Employees, They're People" (February 2002), "What Makes an Effective Executive" (June 2004).