Our focus is on the frequency analysis of LTV systems within the larger context of 2-D analog filtering. The available techniques for characterizing 2-D analog filters are explained. The frequency analysis of 2-D analog systems, based on the classical two-dimensional Laplace transform (2DLT), is outlined. The 2DLT leads to the development of a bifrequency theory for autonomous dynamic systems. The contents of existing literature are complemented more than duplicated.