New technology requirements derived from the exploitation of novel energy resources, and the needs for improvement of the energy efficiency of current power generation systems are pushing the industry towards the search of alternative working fluids. The great challenge for these non-conventional fluids is to provide satisfactory performances and fill the existing lack of media for some innovative energy applications. In this review a number of emerging working fluids for thermal power generation are presented. Also, a special emphasis is devoted to the discussion about new promising fluids, such as nanofluids or ionic liquids, that could be an important breakdown for power generation in the near future.