Using the action principle, and assuming a solitary wave of the generic form u(x, t) = AZ (β(x + q(t)) Periodicals, Inc. Complexity 11: 30-34, 2006 Key Words: action principle; nonlinear field equation; compacton solutions I n a variety of physical contexts one finds nonlinear field equations for which a wide class of solitary wave solutions can exist. However, in many cases one is not able to obtain the solution in a closed form and thus it is not very easy to study the stability of such solutions. In this article we derive a general theorem relating the energy, momentum, and velocity of any solitary wave of a generalized Korteweg-De Vries (KdV) equation of Cooper et al. [1]. The important point is that this particular generalization of the KdV equation is derivable Correspondence to : Avadh Saxena (e-mail: avadh@lanl.gov) from an action principle. Using the theorem, we are able to relate the amplitude, width, and velocity of any of the solitary wave solution even if such a solution is not known in a closed form and also to study its stability. Second, we obtain a two-parameter family of solutions to these equations which include elliptic and hyper-elliptic compacton solutions. For this general family we explicitly verify the theorem as well as the stability criteria.Compactons were discovered originally in an extension