The usability of Free/Libre/Open Source Software (FLOSS) is a new challenge for HCI professionals. Although HCI professionals are working on usability issues in FLOSS, the CHI community has not yet organized with respect to FLOSS. The purpose of this SIG is to bring together HCI professionals and researchers to discuss current issues in FLOSS. Specifically, this SIG looks at usability, the role of HCI expertise, and design rationale in FLOSS projects. Keywords Open Source Software, usability, user-centered design, usability evaluation, design rationale, software development teams. ACM Classification Keywords H5.2. Information interfaces and presentation (e.g., HCI): User Interfaces---Evaluation/methodology, Theory and methods, User-centered design.