This paper discusses the concepts and current trends in the structure of wholesale electricity markets and additionally reviews the structure of some electricity markets in the world. It also reviews the experience around the system operation and market operation, as well as how the main processes are handled in European and American markets. This review shows that there are various designs to which these markets are converging depending on your needs and structures. Some trends turn around the presence of TSO, ISO and market operator (OM); as well as the operation of derivatives markets.