In recent years a number of variants of gas metal arc welding (GMAW) have been developed in an attempt to improve the
performance and productivity of the process. The advent of cost effective electronic power sources has enabled additional
process improvements to be made to the functionality and ease of operation of GMAW. With such a wide range of options now available it is timely to review the developments and assess the potential advantages and limitations of available systems. Since new commercial process modifications seem to be introduced on a regular basis any comprehensive review of all these variants would be quickly superseded and the only way for potential users to assess the options objectively is to understand the basic physical principles of GMAW. The paper discusses these underlying principles and the main groups of GMAW process developments and attempt to clarify their features.