We applied the Input-Process-Output approach and Time, Interaction, and Performance theory to examine the input factors (organisational, group-related, and individual) and process factors (group production, group well-being, and member support) that yield group effectiveness, measured as high-quality articles in Wikipedia. The results provided evidence of the positive effects of: group size and shared experience on both group process variables and group effectiveness; group heterogeneity on group production; organisational support and member activeness on group well-being; member activeness on member support; and organisational support and member activeness on group effectiveness.