High Entropy Alloys are compositionally complex materials, typically containing five or more principal elements in approximately equal atomic ratios. Whilst much of the literature surrounding these materials has been based on combinations of first row transition metal elements, recent publications have identified alloys with promising high-temperature properties based on the refractory metals. Development of these alloys into commercially viable engineering materials requires a detailed understanding of their phase metallurgy, elemental partitioning and information pertaining to the influence of other alloying additions. This project aims to provide such information by establishing the phase equilibria in systematic series of multi-component refractory metal alloys at a number of different elevated temperatures.