Collective bargaining involves a process of negotiation between one or more unions and an employer or employers' organisation(s). The outcome is a collective agreement that defines terms of employment - typically wages, working hours and in-work benefits. The agreement affords labour protection: minimum wages, regular earnings; limits on working hours and predictable work schedules; safe working environments; parental leave and sick leave; and a fair share in the benefits of increased productivity. The International Labour Organization (ILO) Collective Agreements Recommendation 1951 (No. 91) considers, where appropriate and having regard to national practice, that measures should be taken to extend the application of all or some provisions of a collective agreement to all employers and workers included wthin the domain of the agreement. The extension of a collective agreement generalises the terms and conditions of employment, agreed between organised firms and workers, represented through their association(s) and union(s), to the non-organised firms within a sector, occupation or territory. The collection of chapters in this volume are about the extension of collective agreements as an act of public policy.