2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/106687The concept of decoherence is defined, and discussed in a historical context. This is illustrated by some of its essential consequences which may be relevant for the interpretation of quantum theory. Various aspects of the formalism are also reviewed for this purpose. Contents: 1. Definition of concepts. 2. Roots in nuclear physics. 3. The quantum-to-classical transition. 4. Quantum mechanics without observables. 5. Rules versus tools. 6. Nonlocality. 7. Information loss (paradox?). 8. Dynamics of entanglement. 9. Irreversibility. 10. Concluding remarks.19 pages, 3 figures: Talk given at the Seminaire Poincare (Paris, November 2005)- version 2 is a slightly extended and updated version of the proceedings (identical to v1)Quantum PhysicsMesoscale and Nanoscale PhysicsGeneral Relativity and Quantum CosmologyNuclear Theorytext