The primary goal of the proposed CECAM workshop is to facilitate communication and collaboration between users and developers of multi-scale quantum methods, with emphasis on approximate DFT and semi-empirical (SE) methods, linear-scaling quantum mechanical and hybrid quantum mechanical/molecular mechanics approaches. The meeting is intended to provide a unique forum to bring together world leaders of different communities in method development to discuss recent advances in current methodologies, to assess their similarities, and to identify critical challenges in the field as well as future directions for research and development of the next generation of computational tools. On the more technical side, this will include the discussion of the state of the art in efficient parameterization techniques, reference databases, and multi-objective optimization. Simultaneously, the workshop will involve people from the DFT and ab initio communities, who are interested in SE/DFTB methods as a supplement to their first principles codes, for example to use the more approximate quantum techniques for screening large numbers of structures in high-dimensional configuration space and for exploring extended trajectories under real environmental conditions (e.g. deMon2k, ATK, ADF, SIESTA).