The synthesis and structure of organo-inorganic nanocomposites prepared by intercalation of monomers or polymers into the interlayer galleries of layered matrices are analyzed. General features and the mechanism of the intercalation process, as well as materials used for this purpose, mostly often naturally occurring materials (clays, silicates, layered phosphates, chalcogenides, and other moieties hosts), are discussed. Mechanisms governing the intercalation of monomers or polymer repeating units into the interlayer galleries as guests are compared. One of the most widespread and commercially important intracrystalline chemical reactions is the incorporation of monomer molecules into pores or layered lattices of the host substances with subsequent post-intercalation transformations into polymer, oligomer, or hybrid-sandwich products. This strategy is used for the design of organo-inorganic self-assembling nanocomposites as multilayers (P/M)n, where M and P are nanosized oppositely charged layers of an inorganic component and a polymer. Particular emphasis is placed on nanocomposites based on polyconjugated conducting polymers (polyaniline, polypyrrole, etc.) and various mineral matrices, as well as on semiconductor polymer-metal chalcogenide inclusion nanocomposites. Basic application areas of hybrid nanomaterials are considered.