The effective field method is applied to calculation of the effective conductive and elastic properties of matrix composites with different populations of inclusions. The shapes and conductive (elastic) properties of the inclusions are the same inside each population but they are different for inclusions of different populations. Applications of the simplest version of the effective field method (or Mori-Tanaka method) results in the non-symmetric effective conductivity tensor and the elastic stiffness tensor of the composite. The version of the effective field method that allows correcting this drawback is presented in this chapter. In this version, the effective fields that act on the inclusions of different populations are assumed to be different. The effective field method requires construction of two-point correlation functions for random sets of inclusions in hybrid composites. Boolean models of the inclusion sets are used for construction of the correlation functions. The effective elastic properties of a homogeneous host medium with infinite cylindrical fibers and spherical inclusions, cracks, and spherical pores are considered in detail.