Motivated by a desire to discover how buildings operate in practice and inspired by the pioneering PROBE Studies (post-occupancy review of buildings and their engineering) the author has spent the last decade investigating both the design and the users' perceptions of (mainly) sustainable buildings. This has involved visiting some 60 commercial or institutional buildings worldwide, interviewing the designers, and in most cases personally conducting a questionnaire survey of the users covering operational, thermal, lighting, noise, control and satisfaction issues. This paper highlights some of the key findings from these investigations, including the design features of the sustainable buildings, how their performance compared with that of more conventional buildings, whether refurbishments achieved better or worse perception scores than new designs, and the characteristics of the users' comments. The paper concludes by outlining potential approaches to benchmarking user perception scores and advocating for their inclusion in building sustainability rating tools. (C) 2014 Elsevier Ltd. All rights reserved.