The solution of a system of simultaneous linear equations may obtained by inspection of an associated system of nodes and connecting branches called a ‘signal flow-graph’. This provides alternative to conventional algebraic methods which is of particular interest in the case of network analysis, since the flow graph can be set up directly by inspection of the network without having to formulate the associated equations. In the paper the formal theory of flowgraph analysis is developed and applied to certain aspects of feedback theory, and it is shown that the classical results of Bode can be obtained and generalized relatively simply by this approach.