Structural Biology using single particle cryoEM and molecular/cellular cryo-electron tomography (cryoET) has become a major tool for studying macromolecular assemblies that are intrinsically flexible and dynamic, and often function in higher-order assemblies that are difficult to purify. The study of these complexes in situ using cryoET and sub-tomogram averaging at near atomic resolution, coupled with cryoFIB and correlative/integrative imaging, opens a new frontier in structural cell biology, as exemplified in virus infection and bacterial chemotaxis signaling.