This chapter describes international standards for the thermal environment. The International Organization for Standardization (ISO) is the world’s largest standards development organization. ISO standards related to thermal environments are developed by ISO/TC159/SC5/WG1. TC159 is a Technical Committee (TC) on “Ergonomics” and has four active Sub Committees (SCs). SC5 is responsible for “Ergonomics of the physical environment.” WG1, one of the four active Working Groups (WGs) under SC5, is responsible for “Thermal environments.” The scope of ISO/TC159/SC5/WG1 is to develop standards concerning human responses to the thermal environment, effects of the thermal environment on humans (health, safety, comfort, and performance), and methods of evaluation (indices, surveys, and theoretical and analytical methods). ISO/TC159/SC5/WG1 has developed and published 21 standards up to 2025. Typical indices defined in these standards include the Wet Bulb Globe Temperature (WBGT), the Predicted Mean Vote (PMV), the required clothing insulation index (IREQ), and equivalent temperature (teq). In addition to the ISO standards, some other standards are used worldwide, such as ASHRAE Standard 55—Thermal Environmental Conditions for Human Occupancy—published by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). Threshold Limit Values (TLVs®), published by the American Conference of Governmental Industrial Hygienists (ACGIH), include TLVs for heat stress and strain, as well as cold stress. They are also widely used internationally. These standards can be divided into five groups: hot environment, moderate environment, cold environment, application, and supporting standards. This chapter introduces a total of 23 standards by the group.