The aim of this study was to explore the understandings and experiences of self-determination of a group of Mexican young adults with intellectual disability, in particular, how self-determination could be promoted or hindered in dialogue. In this research self-determination is understood in terms of a person’s conscious and intentional decision-making in interaction with a supportive context of opportunities and encouragement. Self-determination theories emphasise interaction and relationality. Moreover, educational programmes to promote self-determination of young adults with intellectual disability commonly rely on interaction between students and educators to set goals and make plans to achieve them. Yet published studies tend to follow individualistic approaches and employ methods that fail to attend to the interaction and relationality of self-determination, and to the young people’s voices and perspectives. The current project aims to contribute to the field of self-determination, internationally and specifically in Latin America where studies on the self-determination of young adults with intellectual disability are scarce. This project also aims to contribute to the field of dialogic theory which has highlighted the need to widen and deepen the understanding of dialogic education through the inclusion of diverse perspectives, and yet has until now left aside the voices and perspectives of people with intellectual disability. This research involved 10 Mexican young adults with intellectual disability who are students at the university-based transition programme: Building Bridges. I facilitated group discussions with these students and three teachers around topics that were of the students’ interest. I also observed naturally occurring interactions of these students with other people in university, work and independent-living contexts. Fieldnotes and verbatim transcriptions were generated. Thematic analysis of the data generated led to the development of six themes that interplay in the students’ decision-making process: decisions, aspirations, preparation, challenges, self-advocacy and supports. Sociocultural discourse analysis of conversations about the students’ ‘Challenge of the Month’ goals showed how the students’ agency (i.e., intentional decision-making) is negotiated in the interaction and how students’ volition (i.e., conscious decision-making) could be promoted through dialogic interactions. Potential constraints on students’ agency and volition development are evident when discussions of concrete courses of action are prioritised over discussions that would lead students to reflect more deeply on the motives behind their goals, and when educators fail to delve into the students' aspirations and decisions and instead propose other 'more viable' options straightaway. This dissertation upholds the importance of studying self-determination as a contextual and relational phenomenon which could be promoted or hindered in dialogue. The findings may encourage educators and researchers to create opportunities for engagement in dialogic interactions with young adults with intellectual disability in order to collaboratively reflect on important life decisions and aspirations and thus promote self-determination.