After having lost population for some decades, many cities are experiencing a new growth. This paper addresses this reurbanisation phenomenon in the case of Switzerland. It argues that the demographic evolution of cities is not adequately explained by the 'stages of urban development' model that tends to consider urban regions as closed systems. It should rather be analysed by unfolding the underlying mechanisms that include housing consumption as well as in- and out-migration flows. Swiss cities have gained inhabitants since 2000 thanks to international migrants, young adults, non-family households and some parts of the middle to upper class. From a demographic point of view, families' residential behaviour remains the driving force of suburbanisation so that the population growth is still higher in suburbs than in cities.