Abstract-This paper presents a formulization of time domain (TD) discrete electromagnetic (EM) solution to provide an effective analysis over a variety of EM problems. This procedure first represents the time responses of EM fields in terms of a set of selected basis functions. Their coefficients are then employed to create matrix-form Maxwell's equations with forms analogous to frequency domain (FD) Maxwell's equations, which allows one to formulate TD solutions via utilizing their corresponding FD solutions that are existing and generally much mature. This work provides general characteristics with parts previously described in the discrete-time EM theory [20,21] and, most importantly, provides rigorous theoretical derivations in formulating the TD solutions.