This book discusses the implementation of sustainability in corporate governance mechanisms since 2013 and assesses how much the role of the Board of Directors has changed as a result. The study explores the impact of legislation upon corporate governance in two European contexts, the UK and Italy, which have been affected differently by changes in national regulations since 2013. This investigation relies first on the analysis of interviews administered to the boards of directors of Italian firms, to highlight how far sustainability objectives were considered a real priority for their firms and how their role evolved in terms of specific duties and practices. Second, thanks to a rich dataset from 2013 to 2017, the investigation considers the corporate governance reports of top Italian and British listed firms, to identify how the integration of sustainability within corporate governance has been evolving since 2013, and how it has been disclosed. This insider perspective provides the reader with a set of tools useful for analysing firms' engagement towards sustainability, and for assessing whether listed firms practice what they preach.