Analysis of grounding systems is rather important issue in the design of lightning protection systems (LPS). Particularly important application is related to LPS for environmentally attractive wind turbines. In general, analysis of grounding systems can be carried out by using the transmission line (TL) model [1, 5, 6] or the full wave model, also referred to as the antenna theory (AT) model (AM) [3, 4, 11]. The latter is considered to be the rigorous one, while the principal advantage of TL approach is simplicity [14]. Both TL and AT models can be formulated in either frequency domain (FD) or time domain (TD) [9]. This paper reviews FD-AT and TD-AT approach, respectively, for the study of horizontal grounding electrode being an important component in many realistic grounding systems of complex shape. The key-parameter in the study of horizontal grounding electrode is the equivalent current distribution along the electrode. Once the current distribution along the electrode is determined, other parameters of interest, such as voltage distribution or transient impedance, can be calculated. Within the AT approach the effect of an earth-air interface is taken into account via the corresponding reflection coefficient thus avoiding the rigorous approach based on the Sommerfeld integrals. The space-frequency and space-time integro-differential expressions arising from the AT model are numerically treated by means of the Galerkin–Bubnov scheme of the Boundary Element Method (GB-IBEM) [9]. Some illustrative FD and TD numerical results for the current distribution and subsequently the scattered voltage along the electrode are obtained.