Lisa Dennison recently left the Solomon R. Guggenheim Museum in New York, where she had worked for nearly 30 years, for Sotheby’s North America. The move set tongues wagging and was taken as yet more proof that leaders in the not-for-profit sector were increasingly gravitating towards commercial enterprises. Dennison was made director of the Guggenheim in 2005, replacing Thomas Krens (who many felt had outstayed his welcome at the helm of the museum), and her departure from the institution has been met with dismay from some – notably a critic on this list – who feel that the museum will flounder without her. Her directorship may have been short-lived but her mettle did not go unnoticed. Tobias Meyer of Sotheby’s personally requested that she join their team, and a position (Executive Vice President of Sotheby’s North America) was created especially for her. Dennison, who counts artists Julian Schnabel, Jeff Koons, Ellsworth Kelly, Richard Serra and Claes Oldenburg as friends, along with collectors Eli Broad and Peter Brant, will be instrumental in helping to boost sales of postwar and contemporary art for the company, which are currently lagging behind those of Christie’s.