AbstractInformation systems success is one of the most widely used dependent variables in information systems (IS) research, but research on free/libre and open source software (FLOSS) often fails to appropriately conceptualize this important concept. In this article, we reconsider what success means within a FLOSS context. We first review existing models of IS success and success variables used in FLOSS research and assess them for their usefulness, practicality and fit to the FLOSS context. Then, drawing on a theoretical model of group effectiveness in the FLOSS development process, as well as an on‐line discussion with developers, we present additional concepts that are central to an appropriate understanding of success for FLOSS.In order to examine the practicality and validity of this conceptual scheme, the second half of our article presents an empirical study that demonstrates operationalizations of the chosen measures and assesses their internal validity. We use data from SourceForge to measure the project's effectiveness in team building, the speed of the project at responding to bug reports and the project's popularity. We conclude by discussing the implications of this study for our proposed extension of IS success in the context of FLOSS development and highlight future directions for research. Copyright © 2006 John Wiley & Sons, Ltd.