Review chapters devoted to the chemistry of 1,4-oxazepines and 1,4-thiazepines appeared in Comprehensive Heterocyclic Chemistry in 1984,1 19962 and 2008.3 The present review, in which we aimed to provide a comprehensive coverage of the 2008–2019 literature related to these heterocyclic cores, should be considered as a logical continuation of the previously published chapters. In addition to monocyclic 1,4-oxazepines and 1,4-thiazepines, we also covered the literature on polycyclic derivatives.