In this study interfacial reactions and electrical properties of Ti, In, Au and W on ZnSe are presented. The combination of these two aspects of contact formation is very useful for the assessment of contact preparation procedures. Firstly the thermodynamic equilibria in the ternary metal-Zn-Se systems were evaluated. Secondly bulk diffusion experiments on the metals on ZnSe crystals were performed. Thirdly the electrical properties of the metal-p-type ZnSe contacts were evaluated and correlated to the results of the phase equilibrium and diffusion studies. Ti and In form ohmic contacts on p-type ZnSe but the mechanism is different. With Ti an interface reaction occurs; with In a solution of surface contaminations in the liquid metal film seems probable. Au and W are not very useful as electrical contacts. Neither reacts with the semiconductor. Au yields irreproducible electrical properties; W contacts show a very bad adherence to the semiconductor.