This volume is the second part of a three-part treatment of the Juncaceae and covers the subgenus Juncus. Almost all the current experts in the taxonomy of the family kindly participated in the project, and their expertise covered both the centres of taxonomic diversity and the most intricate groups in the family. The monograph thus presents the cumulative knowledge of the Juncaceae at this time. Some groups received special attention and their accounts represent new revisions (e.g., Luzula sect. Atlanticae, sect. Alpinae, subg. Pterodes) or recent revisions were incorporated (e.g., Juncus sect. Caespitosi, in part, and Juncus sect. Juncus). The project benefited from an important coincidence: the Juncaceae have been included in recent volumes of important regional or continental floras, either published in 1999 or 2000, or prepared for publication; the authors of several regional accounts participated in this project (including those from Flora of North America, Flora of China, Flora of Australia and Flora Neotropica). Despite this, some groups or sections still require a thorough revision in future, and a number of questions remain unanswered, particularly in Luzula sect. Luzula in China and Japan, Juncus sect. Stygiopsis and Juncus sect. Juncotypus. In addition to the authors and advisers, many other botanists participated in solving problems with old literature, nomenclatural problems and geographical distribution.