We identify two scenarios where the concept of adiabaticity emerges, differing on whether the slow parameters are themselves dynamical variables or not. In both cases, the separation of time-scales leads to synthetic gauge structures that have measurable consequences. We describe the basic theory of adiabatic evolution. Conical intersections, which are points in the space of slow parameters where two or more energies cross, are of central importance for the understanding of the emergent synthetic gauge fields in adiabatic systems.