The idea of the neutrino is about to turn a century old. In this lecture I will recall the fundamental advances that occurred in the 1930s and discuss the major subsequent modifications and evolutions that have shaped modern thinking. I will present a journey through history in six chapters in which I will emphasise particle and theoretical aspects: 1. Pauli's proposal (1930): Meaning of a revolutionary proposal, clarifying the context in which it arose, that of the first theories of the atomic nucleus. 2. Enrico Fermi's theory of interactions (1933): A theory with great potential but also with formal and conceptual limitations. 3. Majorana's treatment of fermions (1937): The origin of the modern treatment of fermions and in particular neutrinos. 4. Progress and subsequent modifications: The discovery of fermion families; the chiral (V-A) structure of weak interactions directly related to the hypothesis of neutrinos with zero mass. 5. Conceptions of neutrino mass and ways to probe them. 6. Prospects for development: the chapter of history we are still writing.