The Cosmological Law of Communication proposes a universal framework in which communication is not a human convention but a fundamental cosmological process governing the emergence, preservation, and transmission of identity and meaning. Building on the four invariants of the ICDP architecture—Information, Continuity, Determinism, and Propagation—the work distinguishes between the interior cosmos of consciousness, identity, and semantic inscription, and the exterior cosmos of matter, universal time, and physical law. The law demonstrates how biological systems, symbolic structures, and engineered communication networks obey the same underlying principles of identity inscription, dependable continuity, causal determinism, and purposeful propagation. By unifying theoretical biology, information theory, and metaphysical cosmology, the book establishes communication as the foundational mechanism through which entities maintain coherence across time and across scales. This contribution reframes communication as a cosmological invariant, offering a new theoretical basis for understanding meaning, agency, and the structure of existence. It positions symbolic communication systems, biological processes, and conscious experience within a single explanatory architecture, advancing a unified cosmology grounded in both scientific and philosophical rigor.