Summary: Several methods exist for converting optimal control problems into parameter optimization problems, and they are categorized by the unknowns of the parameter optimization problem, the numerical integration technique, and the order of the integration technique. Conversion of optimal control problems into parameter optimization problems is accomplished by replacing the control and/or state histories by control and/or state parameters and forming the histories by interpolation. Four general classes of methods exist, and the unknowns in each class are 1) control parameters, 2) control parameters and some state parameters, 3) control parameters and state parameters, and 4) state parameters. In methods of classes 1 and 2, the state differential equations are integrated by explicit numerical integration, and in methods of classes 3 and 4, implicit numerical integration is used. All orders of numerical integration can used in each method.