We show that the connection responsible for any abelian or non abelian Aharonov-Bohm effect with n parallel "magnetic" flux lines in R 3 , lies in a trivial G-principal bundle P → M , i.e. P is isomorphic to the product M × G, where G is any path connected topological group; in particular a connected Lie group. We also show that two other bundles are involved: the universal covering spaceM → M , where path integrals are computed, and the associated bundle P × G C m → M , where the wave function and its covariant derivative are sections.Key words: Aharonov-Bohm effect; fibre bundle theory; gauge invariance.As is well known, the magnetic Aharonov-Bohm (A-B) effect 1,2 is a gauge invariant, non local quantum phenomenon, with gauge group U (1), which takes place in a non simply connected space. It involves a magnetic field in a region where an electrically charged particle obeying the Schroedinger equation cannot enter, i.e. the ordinary 3-dimensional space minus the space occupied by the solenoid producing the field; in the ideal mathematical limit, the solenoid is replaced by a flux line. Locally, the particle couples to the magnetic potential A but not to the magnetic field B; however, the effect is gauge invariant since it only depends on the flux of B inside the solenoid.