A critical review is presented of the advances which have been made in the understanding of coherent-structure development in separated hows and of the implications of these discoveries? theoretical and practical, in the field of combustion. The main emphasis is placed on continuous combustion processes although some of the more general issues discussed relate also to transient situations. Consideration is given first to the purely fluid-mechanical aspects of coherent-structure development, this part of the review covering the findings of linear stability theory, the non-linear stages of instability growth, the development of three-dimensionality and the mixing transition in mixing layers and large structures in turbulent jets. Particular attention is given to questions of mixing and of the implications of coherent structuring for the modelling of reacting flows. Consideration is then given to the various aspects of flame behaviour which have been shown experimentally to be linked to the presence of coherent structures. Particular attention is given here to the ways in which the coherent-structure formation, and thus also the structure and behaviour of the flame, is influenced by the design of the burner equipment. Some of the areas requiring further work are identified and an extensive bibliography is provided.