Defects impact the properties of materials and understanding their atomic structure is critical to their interpretation and behaviour. I will discuss how aberration corrected TEM can be used to resolve the detailed structure of Sulfur vacancies and grain boundaries in CVD grown MoS2 and WS2. I will present our latest results on detecting single Cr and V impurity dopants that substitute Mo and W sites. Electron energy loss spectroscopy is used to map out the spatial position and confirm the contrast profiles from HAADF STEM images. Single Pt atimsnare added to the surface of MoS2 and we study the dynamics of hopping between S vacancies. finally I will discuss in situ observations of Pt nanocrystal formation on MoS2 using high temperature annealing.