This book analyses the historical development of job security regulations in Western Europe from the establishment of freedom of contract in the 19th century until the heyday of two-tier labour market reforms in the 2000s. Job security regulations restrict the managerial capacity to dismissemployees and use new forms of employment such as temporary work when hiring new workers. The book makes four main contributions: First, it shows that trade unions are the main driving force behind the extension of job security regulations because these regulations protect the union organisation in the workplace and award them an important role in company decision-making. Second, theanalysis demonstrates that the extension of dismissal protection was only possible in periods in which the power resources of the labour movement temporarily exceeded those of employers, such as in the immediate aftermath of World War I and II as well as in the late 1960s and early 1970s when a "redwave' swept over Western Europe. Third, the book shows that the trade unions' desire to maintain institutional control caused them to push for the regulation of job security by means of collective agreements. In the medium term, this preference had the paradoxical effect that countries with stronglabour movements featured lower levels of statutory dismissal protection than countries with weak and fragmented labour movements. Finally, the analysis demonstrates that the trade unions' organisational interest in dismissal protection prompted them to assent to two-tier labour market reforms fromthe 1980s onwards, thereby contributing to the dualisation of Western European labour markets.