Karl Linn (March 11, 1923 – February 3, 2005) was an American landscape architect, psychologist, educator, and community activist, best known for inspiring and guiding the creation of "neighborhood commons" on vacant lots in East Coast inner cities during the 1960s through 1980s. Employing a strategy he called "urban barnraising," he engaged neighborhood residents, volunteer professionals, students, youth teams, social activists, and community gardeners in envisioning, designing, and constructing instant, temporary, and permanent gathering spaces in neighborhoods, on college campuses, and at sites of major conferences and events. "Linn is considered 'Father of American Participatory Architecture' by many academic colleagues and architectural and environmental experts of the National Endowm