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Introduction Dry powder inhalers (DPIs), a commonly prescribed inhaler type for respiratory diseases, require patients to generate sufficient peak inspiratory flow (PIF) to ensure optimal drug delivery to the airways. Effectiveness of therapy also requires a good inhalation technique and adequate medication adherence. For patients with chronic obstructive pulmonary disease (COPD), recent studies conducted in tertiary care suggest that DPI users with suboptimal PIF have poorer COPD-related health status and increased exacerbation risk versus those with optimal PIF. The PIFotal study will investigate the impact of PIF, inhalation technique and medication adherence on patient-reported outcomes in patients with COPD in primary care using a DPI for their maintenance therapy. Methods and Analysis This cross-sectional observational study will assess 1200 patients (aged ≥ 40 years, diagnosed with COPD and using a DPI for COPD maintenance therapy for ≥ 3 months) from the Netherlands, Spain, Portugal, Poland, Greece and Australia. Assessments will consist of (1) PIF measurements (usual patient inhalation manoeuvre, maximal PIF against resistance of own inhaler, and maximal PIF against low resistance); (2) Clinical COPD Questionnaire (CCQ), COPD Assessment Test and Test of Adherence to Inhalers scores; and (3) video recordings of patient inhalation technique. Dependent variables include health status (CCQ score), number of self-reported exacerbations in previous 12 months, and healthcare resource utilisation in previous 6 months. Independent variables include PIF values, inhalation technique errors, medication adherence, and demographic and clinical characteristics. In the primary analysis, the mean difference in CCQ score between patients (1) with optimal/suboptimal PIF, (2) exhibiting/not exhibiting inhalation technique errors, and (3) adhering/not adhering to medication will be examined in a multivariable linear mixed model. Ethics The study protocol was approved by ethics committees/institutional review boards of all participating sites prior to enrolment; written informed consent was obtained from all study participants. Trial Registration Number ClinicalTrials.gov: NCT04532853. Supplementary Information The online version contains supplementary material available at 10.1007/s41030-021-00172-7.