Breathlessness that persists despite treatment for the underlying conditions is debilitating. Identifying this discrete entity as a clinical syndrome should raise awareness amongst patients, clinicians, service providers, researchers and research funders.Using the Delphi method, questions and statements were generated via expert group consultations and one-to-one interviews (n=17). These were subsequently circulated in three survey rounds (n=34, n=25, n=31) to an extended international group from various settings (clinical and laboratory; hospital, hospice and community) and working within the basic sciences and clinical specialties. The a priori target agreement for each question was 70%. Findings were discussed at a multinational workshop.The agreed term, chronic breathlessness syndrome, was defined as breathlessness that persists despite optimal treatment of the underlying pathophysiology and that results in disability. A stated duration was not needed for "chronic". Key terms for French and German translation were also discussed and the need for further consensus recognised, especially with regard to cultural and linguistic interpretation.We propose criteria for chronic breathlessness syndrome. Recognition is an important first step to address the therapeutic nihilism that has pervaded this neglected symptom and could empower patients and caregivers, improve clinical care, focus research, and encourage wider uptake of available and emerging evidence-based interventions.