Jagerman (mathematics, Rutgers U.) explains techniques that he has found particularly useful in solving the many practical problems that have been put to him over the years from such fields as engineering, communication, physics, information theory, and astronomy. He presents a theory of difference and functional equations with continuous argument based on a generalization of the Riemann integral introduced by N. E. Norlund, allowing differentiation with respect to the independent variable and permitting greater flexibility in constructing solutions and approximations. He solves the nonlinear first-order equation by a variety of methods, including an adaptation of the Lie-Grobner theory. He also looks at the linear equation with constant coefficients and linear difference equations with polynomial coefficients.