Most of the problems that we have discussed in the book are characterized by scale. In some applications, the benefits of a particular technology are predicated by large scale deployment, and in other applications, our prevailing interest is in developing algorithms to orchestrate the behavior of large scale ensembles of agents. Such issues give rise to new practical and theoretical challenges. Our objective in this part of the book is to briefly touch on these issues, and describe some of the ideas that have been developed and deployed to overcome some of the immediate needs of practitioners.