  Fracton phases exhibit striking behavior which appears to render them beyond
the standard topological quantum field theory (TQFT) paradigm for classifying
gapped quantum matter. Here, we explore fracton phases from the perspective of
defect TQFTs and show that topological defect networks---networks of
topological defects embedded in stratified 3+1D TQFTs---provide a unified
framework for describing various types of gapped fracton phases. In this
picture, the sub-dimensional excitations characteristic of fractonic matter are
a consequence of mobility restrictions imposed by the defect network. We
conjecture that all gapped phases, including fracton phases, admit a
topological defect network description and support this claim by explicitly
providing such a construction for many well-known fracton models, including the
X-Cube and Haah's B code. To highlight the generality of our framework, we also
provide a defect network construction of a novel fracton phase hosting
non-Abelian fractons. As a byproduct of this construction, we obtain a
generalized membrane-net description for fractonic ground states as well as an
argument that our conjecture implies no type-II topological fracton phases
exist in 2+1D gapped systems. Our work also sheds light on new techniques for
constructing higher order gapped boundaries of 3+1D TQFTs.
