Piezo-active composites are regarded as an important group of piezoelectric materials that belong to heterogeneous dielectrics whose physical properties and related parameters depend on many factors. Among the variety of criteria for the classification of piezo-active composites, their microgeometry and connectivity play an important role. Knowledge of the connectivity pattern enables us to carry out a prediction of the effective physical properties and related parameters in terms of micromechanical methods. Piezo-active composites play a key role among modern functional materials due to the considerable electromechanical coupling, piezoelectric activity, sensitivity and anisotropy, and figures of merit. This is achieved in the presence of highly effective ferroelectric components such as poled ferroelectric ceramics and domain-engineered relaxor-ferroelectric single crystals. The properties of the composites are regarded as effective properties in accordance with features of the microstructure, domain structure, arrangement of components and connectivity. The remarkable piezoelectric properties and related parameters of the composites based on ferroelectrics stimulate the creation of novel highly effective materials and are to be taken into account for potential transducer, hydroacoustic, energy-harvesting and other applications.