On its seventy-fifth anniversary, HBR asked five of the business world's most insightful thinkers to comment on the challenges taking shape for executives as they move into the next century. In "The Future That Has Already Happened," Peter Drucker examines the effects of the increasing underpopulation of the world's developed countries. With growing imbalances in labor resources worldwide, he writes, executives in the developed countries will need to improve the productivity of knowledge and of knowledge workers to maintain a competitive advantage. Esther Dyson's article "Mirror, Mirror on the Wall" reveals the mind shift executives will need to make in a networked world, where companies will be known for what they do rather than for what they say. Executives will have to respond openly and intelligently to feedback about their organizations. The old language of property and ownership no longer serves executives, writes Charles Handy in "The Citizen Corporation." The corporation should be thought of no longer as property but as a community, where members are regarded as citizens. Technology has given executives more information than today's machines can help them understand, explains Paul Saffo in "Are You Machine Wise?" Machine-wise executives will know when to turn their computers off and take their own counsel, he writes. Peter Senge's article "Communities of Leaders and Learners" urges executives to reject the myth of leaders as isolated heroes and instead to build a community of leaders. Sustained institutional learning, he writes, requires organizations to reintegrate their typically fragmented learning processes.