These essays not only describe the major changes in British society in recent years, but seek to understand and explain what is happening. They consider the wide variety of mechanisms that underlie these changes, in particular processes of social interaction. The ill-understood nature of these mechanisms may be a major reason why so much social reform has proved ineffective. By highlighting the complexities of the causal mechanisms, sociological research can make a major contribution to policy and public debate. While these papers do not claim that sociology will provide all the answers, they demonstrate that it has made real progress in understanding the social changes that Britain has experienced in recent decades.