To complete the quantum revolution that began with transistors and integrated circuits in the 20^th century requires the development of devices that exploit all the properties of quantum mechanics. Foremost among the challenges are devices that work in the quantum regime, i.e. one photon, one atom, or a few quantized modes of oscillation. Although some truly quantum devices have been demonstrated in laboratory settings, there are very few examples of practical commercial devices. This, then, is a major challenge for 21^st century technology: the construction of platforms and architectures to harness the full power of quantum mechanics through coherent control for practical applications. For solid-state implementations of quantum information processing, the challenges (at the few qubit level) are essentially ones of materials and control. Materials challenges are also vital for what are traditionally considered non-material implementations – e.g. the miniaturization of linear optical quantum computing requires the construction of ultra-low-loss integrated optical circuits, which is a serious materials challenge. Amongst the many potential platforms for practical solid-state quantum devices, diamond is rapidly becoming a material of choice.