The subject of this book is social relations, the concrete ties that are established between individuals, and the networks these ties constitute. Family members, friends, neighbors, business or work colleagues, romantic partners, vague acquaintances: all play a part in people’s lives, helping, influencing, and giving them ideas, but also preventing them from doing certain things. Some they entrust with little secrets and problems; with others they share leisure time and evenings out. When this network changes, life also changes to a greater or lesser extent. Conversely, a significant change in life has repercussions on the individual’s network: he sees less of certain friends and more of others who more closely match new concerns and desires. The aim of this book is to offer an overview of social relations and their dynamics at the level of individuals and their social surroundings. We draw, firstly, on two surveys we carried out and, secondly, on the accumulated findings of the tradition of social network analysis.