  Solar flares and coronal mass ejections are among the most prominent
manifestations of the magnetic activity of the Sun. The strongest events of
them tend to occur in active regions (ARs) that are large, complex, and
dynamically evolving. However, it is not clear what the key observational
features of such ARs are, and how these features are produced. This article
answers these fundamental questions based on morphological and magnetic
characteristics of flare-productive ARs and their evolutionary processes, i.e.,
large-scale flux emergence and subsequent AR formation, which have been
revealed in observational and theoretical studies. We also present the latest
modeling of flare-productive ARs achieved using the most realistic flux
emergence simulations in a very deep computational domain. Finally, this review
discusses the future perspective pertaining to relationships of flaring solar
ARs with the global-scale dynamo and stellar superflares.
