Abstract: On the basis of the theory of concurrent error detection circuits, a new theory of concurrent error location for digital circuits is presented. It includes the definitions of properties of concurrent error location circuits, basic modular structures, and interconnection conditions of modules in basic concurrent error location circuits. A basic concurrent error location circuit is composed of a basic functional module and an error locator. Several properties that characterize the concurrent error location circuits and locators are defined. The interconnection conditions, which the basic functional modules and locators must satisfy to construct basic circuits with different concurrent error location properties, are proved. An example of locators is given to demonstrate the application of the proposed theory.