Eutectic alloys are among the most widely used types of cast metal materials. The stability of their microstructure over a broad temperature range, their low-energy phase boundaries, and their stability of defects make eutectic alloys attractive for industrial applications. Additionally, their good castability provides an advantage from a manufacturing point of view. This fact can be exploited in the field of high-entropy alloys, where the production of bulky ingots is accompanied by complications in the form of segregation and shrinkage. Eutectic high-entropy alloys, in addition to good castability, also possess a suitable combination of increased strength and sufficient ductility. However, to extend and fully exploit the potential of these alloys, it is necessary to validate their behaviour in other technological processes. One such process is fusion welding, where heterogeneous joints are often formed from base materials with different chemical compositions and physical properties. An example is electron beam welding, which is characterised by increased homogeneity of the weld joint, suitable mechanical properties and a low incidence of defects. The present study focuses on the welding of a high-entropy AlCoCrFeNi2.1 alloy together with austenitic stainless steel 1.4571 (AISI 316Ti). The process parameters were initially optimised on a homogeneous material to ensure maximum power density. Subsequently, a heterogeneous joint was formed, the evaluation of which consisted in the observation of the macro- and microstructure, the determination of the chemical composition complemented by phase analysis and the verification of the mechanical properties by hardness testing. The results of the study should provide valuable insights into the behaviour of eutectic high-entropy alloys in fusion welding applications.