Fabricated superconducting circuits can be used to develop quantum bits for a scalable quantum computer. The circuits contain weak Josephson junctions that allow for tunneling of Cooper pairs and weak coupling between superconductors. The number of Cooper pairs and the phase of the superconductor wave function are conjugate quantum variables and they can both be used to define states for the quantum bits. Three types have been developed so far: charge qubits, phase qubits and flux qubits. The status and prospects for further development will be reviewed. Research in Delft on flux qubits will be addressed in more detail.