This book deals with the TIG spot welding in specialist side. Gas tungsten arc welding is an arc welding process that uses an arc between a tungsten electrode (non-consumable) and the weld pool. The process is used with shielding gas and without the application of pressure and is used with or without a filler metal. GTAW is often used for an application that demand high quality welding such as the offshore industry, combined heat and power plant industry, the petrochemical industry, the food industry, the chemical industry and the nuclear industry. An investigation is made to study the effect of welding parameters such as welding current,voltage and time on the weld quality of a thin plate of similar and dissimilar carbon steel and stainless steel. A numerical analysis of TIG spot welding process using finite element method was performed to establish the temperature distributions for similar and dissimilar carbon steel and stainless steel thin plate. Non-linear transient heat analysis using welding parameters such as heat generation and free convection with ambient temperature was performed in order to obtain the temperature.