Increasingly, public sector organizations collaborate to buy products and services. They collectively form purchasing groups to deliver more value for money. What is the progress of these small-scale developments of public sector purchasing groups to date, in the early phases of their life cycle? Although previous research provides general descriptions of life-cycle phases, little attention has been paid to detailed small-scale developments that take place within each life-cycle phase. As a result, little knowledge is available about small-scale developments of purchasing groups. More insight is important in order to better understand how purchasing groups can develop over time from one life-cycle phase into another. Three in-depth case studies from different countries offer a unique comparative overview of small-scale developments in these early life-cycle phases for their five dimensions. Most small-scale problems follow a predictable path, but the way in which the purchasing groups deal with such problems differs depending on the specific situation of the group.