In this article, we present a theoretical framework for mixed reality (MR/XR) self-determined learning to enhance ecological literacy in free-choice educational settings. The framework emerged from a research study in New Zealand which aimed to explore how learning experiences which incorporate mobile technologies within free-choice learning settings can be designed to enhance learner development of marine ecological literacy. An understanding of how mobile technology can be integrated into the teaching and learning of sustainability education that incorporates free-choice learning contexts, such as visitor centres, is of strategic importance to both education outside the classroom and adult learning. Following a design-based research methodology, the framework is presented in the form of a set of design principles and guidelines, informed by key theories in ecological literacy and free-choice learning, heutagogy, bring your own device and self-determined learning. We briefly describe how the framework provided the foundation for an educational intervention. This paper aims to assist researchers and developers of MR/XR immersive learning environments to consider design principles and processes that can enhance learning outcomes within free-choice settings, such as museums and visitor centres.(page number not for citation purpose) learning practically anywhere in collaboration with anyone Pachler, Bachmair, and Cook 2010). They also promote innovative (Parsons 2013), inclusive (Traxler 2010) and transformative (Lindsay 2016) types of learning that challenge traditional teaching and learning approaches (Cochrane 2014;Merchant 2012). The content can be shaped to fit individual characteristics and needs (Aguayo 2016) through self-determined and real-life learning, and within user/learner-generated content and contexts, an approach known as heutagogy (Hase and Kenyon 2013;Luckin et al. 2010;Narayan and Herrington 2014).Recent mobile learning research has emphasised new patterns of connected social learning, and research into the transformative possibilities of digital tools (Cook and Santos 2016). We recognise that learning in the 21st century can occur practically anywhere at any time, in school and out, between students, teachers, non-formal educators and parents/adult learners. Twenty-first century learning outcomes also focus on enhancing access to knowledge and promoting organic and distributed social learning throughout the community, with an awareness that learning can be influenced by technological innovations and affordances (learning possibilities offered by technological tools) (Aguayo and Eames 2017b; Bull, Petts, and Evans 2008; Pachler, Bachmair, and Cook 2010). We also recognise that the sociocultural context provided by educational settings and those within them can build on, disrupt and challenge the personal constructs learners bring to those settings (Aguayo 2016; Rennie and Johnston 2004). A heutagogical approach mediated by mobile technologies could then act to create connections and reinforce lea...