[en] The particular combination of features that are required for a binary system to show useful precipitation hardening is examined. Because this combination is relatively rare, we are not optimistic that many useful binary systems remain to be discovered. When one goes to higher order systems one has much greater opportunities for developing useful systems because of the increased degrees of freedom. The difficulty of understanding what is happening is also correspondingly greater, but if it is possible to properly represent the thermodynamics of the system, then this problem can be resolved. Considerable potential is believed to exist for the development of new alloys containing three or more components