This book constitutes revised selected papers from the 16th and 17th International Conferences on Web Information Systems and Technologies, WEBIST 2020 and WEBIST 2021, which took place virtually in November 2020 and October 2021, respectively. The 10 full papers from WEBIST 2021 and 1 full paper from WEBIST 2020 presented in this volume were carefully reviewed and selected from originally 48 paper submissions in 2020 and 107 submissions in 2021. The selected papers contribute to the understanding of relevant current research trends in Web information systems and technologies, including deep learning, knowledge representation and reasoning, recommender systems, internet of things, Web intelligence and big data.