Book excerpt: Traditionally, city museums have been keepers of city history. Many have been exercises in nostalgia, reflecting city pride. However, a new generation of museums focuses increasingly on the city's present and future as well as its past, and on the city in all of its diversity, challenges, and possibilities. Above all, these museums are gateways to understanding the city—our greatest and most complex creation and the place where half the world's population now lives. In this book, experts in the field explore this 'new' city museum and the challenge of contributing positively to city development.