The search for sound principles for object-oriented languages has given rise to much work during the past two decades, leading to a better understanding of the key concepts of object-oriented languages and to important developments in type theory, semantics, program verification, and program development. The FOOL workshops bring together researchers to share new ideas and results in these areas. The next workshop, FOOL'11, will be held in Portland, Oregon, USA on Sunday, 23 October 2011, during the workshop days at the beginning of SPLASH.