Technological evolution in welding processes and the successful appearance on the market of stainless steel able to operate under extreme services conditions, together with an increasing demand for compact heat exchangers combining efficiency, reliability and versatility, have led to the development, over 25 yr, of all welded plate heat exchangers named and patented under the registered trade name: PLATULAR. This paper gives the background to the introduction of these units, as well as the latest developments in the field of heat transfer: combining multi-streams in a single unit. Some examples are illustrated to more clearly explain the real advantages of this technique.