Book excerpt: This book offers a collection of papers presented at the 2023 6th International Conference on Green Energy and Environment Engineering (CGEEE 2023), held during July 21-23, 2023 in Jeju Island, Korea. Recent studies, promising ideas and new challenges are discussed among environmental engineers, economists and social scientists, demonstrating new paradigms for problem solving and decision making. The book provides researchers and practitioners in the field of in green energy and environmental science with the latest, cutting-edge thought and research in the field. It will appeal to readers interested in these fields, especially those who are looking for new ideas and research directions.