A popular thesis in social stratification argues that the middle class is declining. Our chapter argues that this thesis is flawed both conceptually and empirically. Conceptually, it mixes up the middle and working class and, empirically, misrepresents the trends that shape the class structure. Our chapter discusses the main concepts of class and proposes a model that grasps the class structure of contemporary Western societies. Based on clearer concepts, labour force surveys clearly show that the early 21st century did not see the demise, but the expansion of the (salaried) middle class. Never in history had so many people been working in managerial, professional and technical jobs. By contrast, over the last four decades, the working class experienced a massive employment decline – and this decline had far-reaching consequences. It has vastly reduced its political clout as shown in decreasing trade union density and strike activity as well as in rising income inequality. Moreover, it has led to a fundamental realignment of class voting and contributed to growing family instability. Rather than eroding the middle class, the last decades have put an end to the working-class century.