envelope curve A curve showing the maximum possible outputs obtainable by using a combination of two or more independent processes to pursue any objective. If all processes have constant or increasing returns to scale it is always possible to produce any amount efficiently using only one process. It pays to combine processes only when each has decreasing returns. This can apply to the use of different plants by a firm, or the use of internal production and external trade for a country. The envelope curve is found by taking a graph for one process, and superimposing on it the graph for a second process, using each point on the first process in turn as an origin. The envelope curve is ...