Established in 1998, the Australian National Electricity Market (NEM) interconnects five regional market jurisdictions (Queensland, New South Wales, Victoria, South Australia, and Tasmania). Currently, the NEM supplies about 200 TWh of electricity to Australian businesses and households each year, representing most of the Australian population. Compared with similar networks in Europe and North America, it is both significantly larger in terms of generation and more diverse in terms of generation type, ownership, and structure. Since its establishment in 1988, some of the rules governing the determination of wholesale electricity spot prices in the NEM, including minimum (floor) and maximum (ceiling) prices, have changed markedly. This chapter undertakes an empirical analysis of these changes over the long term, yielding useful findings for the design of new electricity markets and the redesign of existing markets.