THE present investigation aims at basing the subject of Economic Dynamics on clear mathematical foundations as rigorous as those employed in any other branch of dynamics. It is shown that it may be based on postulates in complete formal analogy to those of ordinary dynamics. Economic Inertia and Economic Resilience (and Storage) are then defined and illustrated by examples. Differential equations involving these are next formulated for simple cases corresponding to the ordinary Dynamics of a Particle and it is shown how they enable us to plot curves of economic behavior as functions of time. Some of these curves are found to be oscillatory and others not. In Part II an endeavor is made to state the problem of economic dynamics in a sufficiently general form to permit of the immediate application of the modern methods of dynamical analysis used in physics. It is pointed out that, just as in radiation, we have periodic phenomena in economics, since most of our statistics show economic cycles. Our problem is essentially the same as the physicist's since both may be stated in the same words: "Given a jumble of periodic phenomena, to find an interconnected dynamical system which will parallel the observed phenomena without departing at any point from what we can observe in other manners." An example is worked out illustrating our general dynamical system in a simple way, and the investigation closes with some general observations.