Wang, MHS, and Wang, LK (2022). Cooling tower and boiler water treatment terminologies. In: “Environmental Science, Technology, Engineering, and Mathematics (STEM)”, Wang, LK, Wang, MHS, and Pankivskyi, YI (editors). Volume 2022, Number 2, February 2022; 76 pages. Lenox Institute Press, MA, USA. ISBN 978-0-9890870-3-2…………ABSTRACT: There has been a special partnership of the United Nations Industrial Development Organization (UNIDO) and the US Environmental Protection Agency (USEPA) for transferring the US new and well-established technologies to the developing countries and disseminating the useful technical information to the entire world. This publication is one of many technology transfer documents prepared by the Lenox Institute of Water Technology (LIWT). It introduces the UNIDO, USEPA, LIWT, and the cooling tower and boiler water treatment terminologies. The terminology subjects cover the following areas: the types of cooling tower and boiler, water treatment systems, evaporation, make-up water, blowdown, drift, leakage, cycle of concentrations, ton of refrigeration, water quality parameters, water quality standards, operational problems, scale, biofilm, fouling, corrosion, inhibitors, chemical treatment, non-chemical physical water treatment, physicochemical treatment, green innovations, operation and management (O&M), O&M optimization, water recycle, and water reuse considerations.