A one-dimensional theory based upon fundamental flow relationships is presented for analyzing the behavior of one or more gas streams flowing through a single nozzle. This compound-compressible flow theory shows that the behavior of each stream is influenced by the presence of the other streams. The theory also shows that the behavior of compound-compressible flow is predicted by determining how changing conditions at the nozzle exit plane affect conditions within the nozzle. It is found that, when choking of the compound-compressible flow nozzle occurs, an interesting phenomenon exists: The compound-compressible flow is shown to be choked at the nozzle throat, although the individual stream Mach numbers there are not equal to one. This phenomenon is verified by a wave analysis which shows that, when choking occurs, a pressure wave cannot be propagated upstream to the nozzle throat even though some of the individual streams have Mach numbers less than one. Algebraic methods based on this compound-compressible flow theory are used to demonstrate the usefulness of this approach in computing the behavior of compound-compressible flow nozzles. A comparison of the compound-compressible flow theory with three-dimensional computer calculations shows that the effects of streamline curvature on nozzle behavior can be disregarded for many practical nozzle configurations. Test results from a typical two-flow nozzle show excellent agreement with the predictions from the theory.