Block copolymer (BCP) thin films have attracted significant attention as lithographic templates, separation membranes, and organic photovoltaic active layers for emerging nanotechnologies due to their ability to self-assembly into nanoscale features. To direct the self-assembly of BCP thin film nanostructures, a suite of annealing techniques has been developed (e.g. thermal annealing, solvent vapor annealing, magnetic/electrical field alignment), each with its own set of controllable parameters and mechanisms for nanostructure reorganization. In this Review, we discuss the importance of in situ X-ray and neutron scattering for the study of BCP thin films subjected to different annealing protocols. These scattering approaches have become vital for understanding the complex nanostructure reorganization processes inherent in thin film fabrication and for establishing more consistent control over the morphology, ordering, and orientation. A major advantage of in situ X-ray and neutron scattering characterization is the ability to link the thermodynamic and kinetic pathways of nanostructure evolution over macroscopic (several cm(2)) areas during annealing or processing. This feature has made in situ X-ray and neutron scattering ideal for refining annealing techniques, fostering robust assembly protocols, and developing the next-generation of directed assemblies. As the toolbox of viable processing methods continues to grow, we highlight potential opportunities to enhance current X-ray and neutron scattering capabilities through the improvement of scattering facilities, techniques, sample chambers, scattering/annealing protocols, and model development to establish universal control over BCP thin film self-assembly. (C) 2016 Elsevier Ltd. All rights reserved.