The private collector's museum has become a phenomenon of the 21st century. There are some 400 of them around the world, and an astonishing 70% of those devoted to contemporary art were founded in the past 20 years.

Although private museums have been accused of being tax-evading vanity projects or 'tombs for trophies', the picture is far more complex and nuanced, as art-market journalist Georgina Adam (author of best-selling Big Bucks and Dark Side of the Boom) shows in her compelling new book.

Georgina Adam's investigation into this extraordinary proliferation, based on her recent visits to over 50 private spaces across the US, Europe, China and elsewhere, delves into the reasons behind this boom, the different motivations of collectors to display their art in public, and the various ways in which the institutions are financed.

Private museums can add greatly to the cultural life of a community, giving a platform to emerging artists, supplying educational programmes and revitalising declining or neglected regions. But their relationship with public institutions can also be problematic.

Should private museums step in to fill a gap left by declining public investment in culture, and what are the implications for society and the arts? At a time of crisis in the museums sector, this book is an essential and thought-provoking read.