The new notion of fusion frames will be presented in this article. Fusion frames provide an extensive framework not only to model sensor networks, but also to serve as a means to improve robustness or develop efficient and feasible reconstruction algorithms. Fusion frames can be regarded as sets of redundant subspaces each of which contains a spanning set of local frame vectors, where the subspaces have to satisfy special overlapping properties. Main aspects of the theory of fusion frames will be presented with a particular focus on the design of sensor networks. New results on the construction of Parseval fusion frames will also be discussed.