Orthogonal Functions may be divided into two classes. The class of continuous systems and the discontinuous class of piecewise constant systems. Problems arise because continuous systems form an unsatisfactory basis for the expansion of functions containing discontinuities whilst piecewise constant systems insert artificial discontinuities into all representations. Since these two classes of functions would be unsuccessful in coping with functions that possess both continuity and discontinuity we must look to General Hybrid Orthogonal Functions (GHOF) which have been shown to be the most appropriate in such situations. This book introduces the system of GHOF, discusses its properties, develops an operational algebra for the discretization of continuous dynamic systems on the system of GHOF and illustrates its use as a flexible and powerful framework of computational tools in a wide range of systems and control.