热学又称热物理学，是研究热现象（即与温度有关的物理现象）的科学。

热学一般分为热力学和统计力学两部分，前者是创建在实验基础上的宏观理论，后者是创建在量子力学和数理统计学上的微观理论。

热学是从18世纪末才发展起来，主要是研究功与热之间的能量转换。在此功会被定义为力与位移的内积；而热则定义为在热力系统边界中，由温度之差所造成的能量传递。

Thermal physics is the combined study of thermodynamics, statistical mechanics, and kinetic theory. This umbrella-subject is typically designed for physics students and functions to provide a general introduction to each of three core heat-related subjects. Other authors, however, define thermal physics loosely as a summation of only thermodynamics and statistical mechanics.