This book addresses the question of ageing and declining technologies, induced or not, and bets on the fact, that there is much to gain in looking closely at the activities entailed. Dismantling, decommissioning, deconstruction, closing-down, phasing-out, discontinuation, redirecting are all operations that are key to numerous industry sectors and high-hazard activities. Why? Because they represent a form of undoing that may prove to be key in redirecting vast industrial sectors, in light of climate change urgent transition. These operations are rarely the most “glamorous” phase of a system’s lifecycle, and may even constitute a form of taboo in some industry sectors. Depollution and waste management are usually envisioned as a mal necessaire, rather than as an expected and intentional industrial phase, from which may emerge precious knowledge, expertise and know-how. This book proposes a different approach and a side step, considering that there are different ways to go about decline. The contributors, drawn mainly from academic backgrounds, embarked on the idea that there is much to learn from these phases, also because as the chapters will show, they are replete with surprises, treasures, uncertainties, and reversals. This eight-chapter academic book is based on presentations and earlier drafts by international experts who were invited in January 2024 to the 37th workshop under the auspices of NetWork (New technologies and Work), supported by FonCSI, a French public-interest research foundation. It deals with issues of interest to researchers and graduate students in safety science, transition studies, science and technology studies, organization and management studies, and anthropology, as well as to members of expert bodies and experts in industry and consultancy concerned with similar subjects.