Cities have always been built by their citizens. For millennia this was literally so and our cities have grown though myriad forms of participation and creativity into a brilliant synthesis of the ideas and actions of millions. The exponential growth of the modern city has also inadvertently estranged us from a role in shaping it. For many, the city seems just too big, too intractable, too inaccessible. But around the world, scores of people and organizations are intervening directly in their own environments, bringing incremental improvements to their streets, blocks, and neighborhoods. These acts of micro-urbanism, of informal urban design, are characteristically small in scale, and often temporary—the opposite of the qualities we traditionally associate with good design—yet their power resides not so much in their forms as in their impacts, in their immediate ability to infuse places with value and meaning.