This paper explores the complex relationship between structure and agency and the way it has been incorporated into migration theory. It argues that attempts to develop a coherent and robust body of migration theory have been thwarted by a structure/agency impasse: some approaches lean too close to functionalism while others veer into structuralism. Those who search for middle ground have tended to draw on Giddens' notion of structuration as a way of articulating the balance between structure and agency in migration processes. The article shows that, while structuration is beguiling, it has failed to offer any significant advances for migration theory. This is a result of theoretical weaknesses in structuration theory rather than a failure of its application; this argument is based on a critical realist critique of the dualism inherent in structuration. It is suggested that critical realism offers a fruitful avenue for a more sophisticated analysis of structure and agency in migration processes. The article ends with a brief outline of a critical realist approach to migration theory and argues that this may offer a way around the structure/agency impasse.