This volume constitutes the proceedings of the 27th International Conference on Collaboration Technologies and Social Computing, CollabTech 2021, held August/September 2021. Due to VOVID-19 pandemic is was held virtually. The 5 full and 4 work-in-process papers presented in this volume were carefully reviewed and selected from 19 submissions. The papers focus on innovative technical, human and organizational approaches to expand collaboration support including computer science, management science, design science, cognitive and social science.