First published in 1999, this volume responds to a large and growing interest among health policy and research circles on the use of purchasing alliances to leverage change in health care. This book gives detailed and useful specifics on how a leading alliance has fared in California, the most competitive health care market in the United States. Although it is generally accepted that large organizations are more effective purchasers of health insurance, little work has been done to carefully examine the reasons that underlie that phenomenon. Yet, creating interventions and designing potential solutions requires a thorough understanding of the issues. The econometric analysis adds to the limited literature on the influence of premium on choice behaviour for employees of small firms, and introduces an analysis of choice behaviour in a purchasing cooperative setting. The political section of this book presents a much more detailed historical account and analysis of California’s small group market reforms, the most significant health-related legislation in the state in the prior decade, than has been previously available. The conclusions are becoming particularly relevant, both in California and elsewhere, as the issues of reform of the individual market for health insurance comes to the forefront.