Hot disk metrology represents a transient plane source measurement technique for characterizing thermal conductivity and thermal diffusivity of a wide range of materials. In this technique, the hot disk sensor serves as a heat source and a thermometer. During the measurement, the sensor is sandwiched between two halves of a sample and a constant current is supplied to the sensor. The temperature increase at the sensor surface is strongly dependent on the thermal transport properties of the surrounding material. By monitoring the temperature increase as a function of time, one can determine the thermal conductivity and thermal diffusivity of the surrounding material. The main advantages of the hot disk technique include: wide thermal conductivity range, from 0.005 W/m·K to 500 W/m·K; wide range of materials, from liquid to solid; easy sample preparation; non-destructive; and more importantly, high accuracy (within 2% or better). In this paper, the basic theory of the hot disk technique will be discussed based on first principles. This technique has been successfully used to characterize a variety of thermal interface materials (TIMs) used in electronic packaging. The experimental results are in good agreement with the results obtained by another method.