The energy consumption worldwide will increase for the coming decades. In order to address global warming, international experts agree that no low CO2 emitting energy production routes should be omitted. In fact, nuclear energy production is appointed an important role in the transition towards a low CO2 emitting world. Taking into account the identified reserves of uranium and assuming a stable consumption of uranium in light water reactors, the uranium reserves will surely fit for one or two centuries. However, by switching to another fuel cycle using uranium in fast reactors, the uranium reserves may serve the world for a multi-fold of centuries. Nowadays, the most mature fast reactor designs are liquid metal cooled fast reactors.Design support and safety analysis of liquid metal reactors strongly relies on thermal hydraulic simulations and experiments. This paper will discuss the current state-of-the-art in liquid metal thermal hydraulics and also its future perspectives. In particular, the following topics will be discussed: liquid metal heat transfer, fluid-structure interaction, fuel assembly thermal hydraulics, coolant solidification, efficient 3-d system modelling, and validation at large. For each topic, the state-of-the-art, challenges and the future perspectives will be described from the author’s point of view.