Indium nitride is a new narrow gap semiconductor (<0.7 eV), which, alloyed with GaN (3.5 eV) and AlN (6.2 eV), will allow the spectral range from telecom to hard UV wavelengths to be covered. This narrow band gap makes InN an exciting material from which to develop the highest efficiency solar cells. Moreover, due to an electron mobility of around 4000 cm2/Vs and very high saturation velocities, InN is an ideal material for the development of high electron mobility devices capable of operating in the Terahertz range. To ensure the production of reliable commercial devices, rigorous fundamental research is required to understand the layer growth mechanisms and optimize material properties. In the RAINBOW academic and industrial consortium, the theoretical work will encompass modelling of the atomic structure and properties of the material from empirical potentials to ab initio techniques. Experiments will provide correlated structural, electronic, optical and chemical information from the nano to the macroscopic scale. In a closely concerted effort, we will determine the best conditions for the growth of highest quality InN and In rich (In,Ga,Al)N alloys by the main growth techniques (MOVPE, PAMBE, and HVPE). Under the supervision of world leading experts, numerous ER/ESRs will directly benefit from this interdisciplinary and multisectorial research and training effort. The ER/ESRs involved in this programme will also learn to manage research and industrial projects