This study explores the concept of 'STEM belonging' among socio-demographically diverse students at the A-level, undergraduate, and postgraduate levels in England. The research aims to understand how students define and experience belonging in STEM fields, particularly focusing on gender and ethnicity. Through an inductive thematic analysis of 313 participants, the study reveals that female, non-binary, non-White, and first-generation students often define STEM belonging as feeling safe and comfortable in the STEM community and settings. This theme encompasses the group, community, and learning environment, emphasizing the importance of interaction and comfort. The study conceptualizes STEM belonging into four phases: adaptation, integration, continuum, and transition, which are interconnected and form a cumulative cycle. Key themes include feeling safe and comfortable, shared passion and interest in STEM, building social connections, receiving support, and maintaining resilience. The findings highlight the need for supportive and welcoming environments to foster a sense of belonging, which is crucial for academic achievement and persistence in STEM fields. The study concludes that a sense of belonging is influenced by both intrinsic factors (e.g., motivation, beliefs) and social determinants (e.g., social support, social capital).This study explores the concept of 'STEM belonging' among socio-demographically diverse students at the A-level, undergraduate, and postgraduate levels in England. The research aims to understand how students define and experience belonging in STEM fields, particularly focusing on gender and ethnicity. Through an inductive thematic analysis of 313 participants, the study reveals that female, non-binary, non-White, and first-generation students often define STEM belonging as feeling safe and comfortable in the STEM community and settings. This theme encompasses the group, community, and learning environment, emphasizing the importance of interaction and comfort. The study conceptualizes STEM belonging into four phases: adaptation, integration, continuum, and transition, which are interconnected and form a cumulative cycle. Key themes include feeling safe and comfortable, shared passion and interest in STEM, building social connections, receiving support, and maintaining resilience. The findings highlight the need for supportive and welcoming environments to foster a sense of belonging, which is crucial for academic achievement and persistence in STEM fields. The study concludes that a sense of belonging is influenced by both intrinsic factors (e.g., motivation, beliefs) and social determinants (e.g., social support, social capital).