Plasma spraying is often assumed to be a mature technology in which all the important phenomena have been observed and described adequately. However, the intricate interactions between the electrically conducting fluid and electromagnetic, thermal and acoustics phenomena that affect the operation of the plasma torch are not fully understood as yet. Also, variants of the plasma spray process are emerging and raise new scientific questions. These technologies include the spraying of liquid feedstock in the form of submicrometric particles or chemical precursors in a solvent and, coatings formed by vapor condensation onto the substrate. These relatively novel techniques make possible the production of thinner coatings than in air plasma spraying with a fine and even nanostructured microstructure. This paper attempts to define some of the current important issues and research priorities in the plasma spray field.