The 2007 Monograph cogently pointed out that CPET should be viewed as an adjunct to previous comprehensive medical evaluation comprising of: medical history, physical examination and, according to the specific clinical scenario, appropriate complementary tests (e.g. haematocrit, resting ECG, chest imaging, arterial blood–gas and acid–base status, resting pulmonary function, echocardiography) [4]. Thus, there is a key interpretative feature of CPET which, if ignored, may constitute an important source of frustration for the requesting physician: the test should always be interpreted in the light of the pre-test likelihood of abnormality. In fact, many patients referred for CPET have undergone extensive investigations, including chest computed tomography, transthoracic echocardiography and measurement of circulating biomarkers (e.g. troponin, brain natriuretic peptide). It is therefore the referring physician’s task to integrate the described pattern(s) of dysfunction into his/her diagnostic plan or prognostic assessment. This has become even more relevant in the past decade as the “typical” patient currently referred to CPET has multiple comorbidities in addition to polypharmacy, obesity and extreme sedentarism. It follows that the individual showing a single mechanism of exercise intolerance has become exceedingly rare in the CPET laboratory. In this challenging scenario, this Monograph aims to provide a comprehensive update on the contemporary uses of CPET to answer clinically relevant questions in respiratory medicine. This introduction to the Monograph provides a succinct overview of the key extant gaps in knowledge the application of CPET-based investigations in these gaps might prove valuable to the improvement of patient care. What are the specific scenarios in which CPET has advanced the provision of clinically relevant information in the past decade? Investigating exercise intolerance Dyspnoea as a cause of exercise intolerance In respirology practice, CPET is now more commonly requested as part of the work-up for unexplained or disproportionate exertional dyspnoea [5–13]. As discussed elsewhere in this Monograph [14], the test is more suited to describing patterns of dysfunction, as different clusters of abnormalities overlap across specific diseases. CPET fundamentally aims to shorten the list of differential diagnoses that could explain a patient’s symptoms in some circumstances, it also helps guide further investigations. Results might also give reassurance that major dysfunction is not currently impacting on exercise responses. In patients with known cardio-respiratory diseases, gaining insight into the pathophysiology of dyspnoea and exercise limitation might prove valuable to clinical decision making, particularly in patients with only mild-to-moderate disease. CPET may help clinicians unmask the physiological mechanisms (and their interactions) underlying this symptom in a broad spectrum of cardio-respiratory disorders (figure 2) [6]. The test may also help clinicians identify additional mechanisms leading to dyspnoea deemed “independent of” or “not directly related to” the disease under consideration. It can also be used to explore the mechanisms by which exertional dyspnoea can be ameliorated after pharmacological and non-pharmacological interventions [15] a chapter by O’DONNELL et al. [16] in this Monograph considers this area further. Recognition that useful insights into the mechanical underpinnings of dyspnoea are gained by following the operating lung volumes [17] has proved important in enhancing the test’s https://doi.org/10.1183/2312508X.10015318 xi