Great efforts have been made to develop the ability to accurately and quickly predict the durability and reliability of vehicles in the early development stage, especially for welded joints, which are usually the weakest locations in a vehicle system. A reliable and validated life assessment method is needed to accurately predict how and where a welded part fails, while iterative testing is expensive and time consuming. Recently, structural stress methods based on nodal force/moment are becoming widely accepted in fatigue life assessment of welded structures. There are several variants of structural stress approaches available and two of the most popular methods being used in automotive industry are the Volvo method and the Verity method. Both methods are available in commercial software and some concepts and procedures related the nodal force/moment have already been included in several engineering codes. Works have been conducted to compare the similarity and difference in predicted results from these two methods in terms of data correlation. However, the similarity/difference of the underlying theories of these two methods are not available to most practitioners. In fact, it has not been systematically studied. To better utilize the methods in engineering design and to build confidence in these nodal force/moment based methods, a basic understanding of the underlying principles, the concepts, the theories, and the stress and life evaluation procedures are strongly desired.In this paper, the development histories of these methods are reviewed first. Subsequently, the underlying fundamental theories are described and compared in details. The similarity and difference between these two methods in the basic theories are highlighted. Finally, several simple case studies with easy hand calculations are provided, and examples for fatigue life assessment of several complex welded structures are also demonstrated.