This presentation focuses on the structure and energetics of line defects in 2D materials and their impact on microstructures. We employ several approaches in which local bonding information is determined using first principles methods, continuum methods are employed to describing in-plane strain and bending, and microstructures are described with phase field methods and/or Peierls-Nabarro models. I will focus on applications in bilayer systems (interlayer dislocations and twisted (Moire) layers) and a single layer case where multiple phases can co-exist in a single layer (e.g., TMDs). A recurring theme is the interplay between stress, phase, and buckling.