The presented book covers all aspects of green chemical engineering and technology research, with an aim to provide an overview of the scientific, economic and environmental issues especially in green economy. All papers are green technology-related, specifically to environmental, sustainable and clean technologies; bioengineering (bioprocesses, biocatalysts, and bioproducts); food and agricultural based technology and products; polymers, catalysis and advanced materials; forensic science and biotechnology; process designs, integration and optimization; process modelling, safety and health; and renewable energy. The articles were collected by the results of the 5th International Conference on Green Chemical Engineering and Technology 2021 (5th GCET 2021, December 2021, Malaysia), a biannual international conference that began in 2013. It demonstrates the Universiti Kuala Lumpur Branch Campus Malaysian Institute of Chemical and Bioengineering Technology (UniKL MICET) full commitment to enhancing research and development activities in green technology and related areas.