Since the first observation, almost 15 years ago, of coherent oscillations in a superconducting qubit there have been significant developments in the field of superconducting quantum circuits. With improvements of coherence times by over 5 order of magnitude, it is now possible to implement simple quantum algorithms with these circuits. In parallel to these developments, much effort has been invested in using superconducting qubits as artificial atoms to explore quantum optics in unconventional parameter regimes. After a short introduction to superconducting quantum circuits, we will consider a situation where several (artificial) atoms are coupled to a one-dimensional superconducting transmission line. Since microwave photons can travel without loss for a long distance along the line, real and virtual photons emitted by one atom can be reabsorbed or scattered by a second atom leading to collective behaviour. Comparison of these theoretical results to experiments realized by the ETH Zurich group will be presented.