The papers in this Special Supplement are based on research funded by the participating members of the joint Center for Health Management Research (CHMR) and Center for Organized Delivery Systems (CODS), and supported by the National Science Foundation under its Industry-University Cooperative Research Center Program. This 3-year research initiative from 1996 through 1999 involved 69 physician organizations (primarily organized medical groups as opposed to IPAs) associated with 14 organized delivery systems. The groups ranged in size from three to 958 with an average size of 76.4 and a median size of 25.0. Comparisons of the study groups with United States physician groups overall are shown in Table 1. The study groups are larger and more likely to be multispecialty than all groups in the United States. The organized delivery systems range in size from one hospital to 80 hospitals with an average of 21 hospitals per system and a median of 11 hospitals per system. They average 4.6 affiliated medical groups with a range from one to 23. The organized delivery systems range in total revenues in 1998 from $340 million to $6.2 billion with an average of $2.1 billion. All the study systems are not-for-profit. Most are located in single market areas, but several are located in multiple markets. For the most part, they represent some of the larger most experienced organized delivery systems in the country. Among the primary objectives of the study was to identify the factors most strongly associated with physician alignment with the health care system and the consequences for the implementation of evidence-based care management practices. The study was also designed to identify the barriers and facilitators to achieving such alignment and its consequences.