What makes a building green? Can claims to be "green" be believed? This study attempts to identify the criteria used by clients, developers, designers and building users to justify green claims on a number of existing buildings. It reports the findings of a questionnaire survey of building owner/operators, developers/contractors, architects and consultants. The study aimed to establish how people who claimed to have a "green" building justified those claims; industry perceptions of the importance of a wide range of environmental issues; and strengths and weaknesses in current guidance.