The concept and theory of the

th-order inverse of a nonlinear system es developed in this article. The

th-order inverse,

, of a system

is defined as a system for which the Volterra series of the system

formed by the tandem connection of

and

is
![Q[x]= x+ \\Sigma _{n=p+1}^{\\infty } Q_{n}[x]](/images/tex/10326.gif)
so that the 2nd through the

th-order Volterra operators of

are zero. The necessary and sufficient conditions for the existence of

are determined. It is shown that the

th-order pre-inverse of a system

is identical to its

th-order post-inverse. In addition, a synthesis of

is obtained. The

th-order inverse offers an approach to the study of the system inverse,

, since, as

becomes the Volterra series of

. This approach is discussed and some applications with regard to nonlinear differential equations and nonlinear feedback systems are presented.