Background/Objectives: Diabetes mellitus (DM) is a group of chronic metabolic disorders characterised by persistent hyperglycaemia and an increasing global prevalence, imposing a significant socioeconomic and healthcare burden. Among its associated complications, the diabetic foot is a critical condition that doubles the risk of mortality. Although therapeutic footwear is an essential preventive strategy, research on treatment adherence has predominantly focused on quantitative parameters. This protocol aims to explore the experiences, needs, and perceived barriers of people with DM regarding therapeutic footwear use from a qualitative perspective. Methods: A qualitative focus group study will be conducted in the province of Alicante, Spain. Participants will be adults with a confirmed diagnosis of DM recruited across IWGDF foot risk categories 1–3 through purposive sampling. A total of 8–10 focus groups of 10–12 participants will be conducted in separate in-person and online modalities. Data will be analysed using reflexive thematic analysis within a constructivist epistemological framework, following the six-phase approach proposed by Braun and Clarke. The study adheres to the Consolidated Criteria for Reporting Qualitative Research (COREQ). Ethical approval will be obtained from the relevant Ethics Committee prior to data collection. Results/Expected Outcomes: The findings are anticipated to generate patient-centred, evidence-based insights into the psychosocial and experiential dimensions of therapeutic footwear adherence, informing the development of novel educational strategies and improvements in footwear design to optimise treatment adherence and clinical outcomes. Conclusions: This protocol provides a rigorous and transparent methodological framework for qualitative investigation of therapeutic footwear adherence in people with DM, contributing to a more comprehensive and person-centred approach to diabetic foot prevention.