Thermal analysis is one of the cardinal studies essential for arc welding processes. Thermal field and temperature distribution in arc welds affect the quality of welds as they govern the microstructural and thermo-mechanical properties. Therefore, thorough understanding of the thermal behaviour in arc welds is an absolute necessity. Significant efforts have been made in the past to determine the temperature field associated with arc welding. However, for accurate determination of the temperature field/distribution, it is necessary to understand the heat source which influences the temperature distribution in welds. Rosenthal reported the first concept of modelling the heat source, which was then improvised and new models have been instituted through the years. This review article summarizes a collective study made on the heat source and the resulting temperature distribution in arc welds. Numerous methods have been developed to conduct transient temperature distribution studies on arc welds. Analytical approaches with constant material properties, numerical approaches with variable material properties, infrared imaging systems, machine vision systems with soft computing, etc. have been developed to facilitate understanding of transient temperature in arc welds. We first summarize heat source studies followed by literatures on various techniques and methods devoted to transient temperature investigations. Eventually, latest methods used for thermal studies, such as image processing, machine learning and intelligent systems are summarized and discussed.