Decoherence {#Deco}
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In recent years, decoherence has become an extremely popular subject, both in applied and fundamental physics. In the former, decoherence is a subject of enormous relevance, as the effect is one of the main concerns in the practical development of quantum computers as well as in other interesting experimental proposals. In the latter, it has often been promoted as the solution to long-standing foundational problems. In particular, decoherence is deemed to solve (at least important parts of) the measurement problem and to explain the quantum-to-classical transition. The idea is that decoherence, which is a straightforward consequence of a purely unitary evolution, is able to effectively explain or bring about the collapse of the wave function, which is, of course, at the root of the measurement problem. Similarly, decoherence is said to dynamically single out a preferred basis, which is supposed to coincide with the classical one, thus explaining the emergence of classicality. The objective of this section is to carefully show that, contrary to widespread believe, decoherence does not help in the resolution of these foundational questions. The main reason being, as we will see below in detail, that in order for decoherence to accomplish what it 