In this paper we report on a research project that is seeking to develop a more sophisticated theoretical understanding of how and under what conditions mathematics teachers learn to effectively integrate technology into their practice. The aim of the project is to identify and analyse individual and contextual factors influencing secondary mathematics teachers' use of technology, and compare ways in which these factors come together to shape teachers' pedagogical identities. To do this we have undertaken longitudinal case studies of four secondary school mathematics teachers who were selected to represent contrasting combinations of factors known to influence technology integration Analysis of the data is from a sociocultural perspective, using Valsiner's zone theory as the theoretical framework. We compare similarities and differences between the teachers' professional identities to understand how these might influence the extent to which they adopt innovative practices involving technology. This provides a picture of each teacher's professional identity as an individual-acting-in-context.