Even though many of the essential notions of hypertext were first contained in the description of a “memex,” written by Vannevar Bush in 1945 [Bus45], there are today only a few scattered implementations of hypertext, let alone any serious use of it in a CAD environment. In what follows, we describe what hypertext is all about. We describe a prototype hypertext system, named Neptune, that we have built. We show how it is useful, especially its broad applicability to CAD.