Electrons in a superconductor form Cooper pairs and thus condense into a ground state which can be described by a macroscopic quantum wavefunction. The phase of the wavefunction represents a collective movement of millions of Cooper pairs. Using devices based on Josephson tunnel junctions we are able to control and detect the phase and number of Cooper pairs in a superconductor. Josephson devices are therefore excellent systems for demonstrating macroscopic quantum phenomena. We present a short review of the macroscopic quantum phenomena in superconducting Josephson devices, as well as their applications and prospects in quantum computationl.