The role of the structural peculiarities of electrically conductive polymer composites is considered in this review. Different conceptions of the nature of the conductivity and the mechanisms of charge transfer in heterogeneous structures are presented. Experimental results obtained by different scientists are only partially in accord with existing theoretical models. It is suggested that lack of information on various physical and chemical factors influencing the processes of electrical current formation in polymer composites is one of the main reasons for the divergence between theory and experimental results, among which the rate of the inter-and intra-phase interactions in composites may be considered very important. The conductivity of systems with binary conducting fillers is also considered.