This first comparative-historical analysis of the regulations that restrict the managerial capacity to dismiss employees and use temporary forms of employment addresses four puzzles that have long troubled the comparative political economy literature. Who is the driving force behind the extension of dismissal protection? Why is statutory dismissal protection particularly extensive in continental Europe? How can the uneven temporal development of job security regulations be explained? And what are the causes of the two-tier labour market reforms in recent decades? Analysing the historical development of job security regulations in Western Europe from the establishment of freedom of contract in the 19th century until the peak of two-tier labour market reforms in the 2000s, this book contributes to resolving these puzzles by emphasising the important role of trade unions, their preference for institutional control, and the strategic choices they make.