The role of quantum mechanics in large systems raises some very interesting questions. Can local realism be violated using large numbers of photons? Can particle-like behaviour be seen in optical states containing 1000s of photons (analogous to wave-like behaviour of large molecules)? And are there fundamental limits on the size, and therefore utility, of quantum systems, given the role of decoherence? We aim to answer fundamental questions like these to understand quantum mechanical effects as the scale approaches our every day experience of the world. As well as being interesting in its own right, this is crucial to unlocking the huge potential of quantum mechanics for a variety of applications.