The compact city has become a leading concept in the planning of peri-urban areas. The compact city concept is often advocated as "sustainable" because of claims that include lower emissions and conservation of the countryside. The literature shows, however, that there are certain trade-offs in striving for compaction, especially between environmental and social aspects of sustainability. In this article, we describe expressions of the compact city concept in the planning practice of several European urban sample regions, as well as policies and developments that contradict the compact city. We look at examples of positive and negative impacts of the compact city that were observed in the sample regions. Further, we discuss attempts by planners to deal with sustainability trade-offs. Being aware that developments in the peri-urban areas are closely connected to those in the inner city, we compare the sample regions in order to learn how the compact city concept has been used in planning peri-urban areas across different contexts in Europe: in Western, Central and Mediterranean Europe, and with growing, stable or declining populations. We conclude with recommendations with respect to balance in applying the compact city concept.