Nagase T., Todai M., Wang P., et al. Design and development of (Ti, Zr, Hf)-Al based medium entropy alloys and high entropy alloys. Materials Chemistry and Physics, 276, 125409. https://doi.org/10.1016/j.matchemphys.2021.125409. The design and development of TiZrHfAl medium entropy alloy (MEA), and the TiZrHfAlNb0.2 and TiZrHfAlV0.2 high entropy alloys (HEAs) is described. The combination of 4th subgroup elements (Ti, Zr, and Hf) with Al is discussed based on the periodic table and taxonomy of HEAs. The alloys were designed using alloy parameters for HEAs, predicted ground state diagrams from the Materials Project, and the calculation of phase diagrams (CALPHAD). Rapid solidification was effective to suppress the formation of intermetallic compounds, resulting in BCC/B2 phase formation. Significant differences in the constituent phases and Vickers hardness between ingots and melt-spun ribbons were found among the TiZrHfAl MEA, TiZrHfAlNb0.2, and TiZrHfAlV0.2 HEAs.