This book constitutes the refereed proceedings of the Third International Conference on Quantitative Ethnography, ICQE 2021, held in November 2021. Due to the COVID-19 pandemic the conference was held online.  The 26 full papers were selected from the 60 submissions. The contributions in this volume come from diverse fields and perspectives, and present the studies on advantages of using quantitative ethnography methods and techniques in a number of different domains and contexts, including ethnography and statistics, human interpretation and machine processing, etc.