Pulmonary hypertension (PH) is defined by an increased mean pulmonary artery pressure (PAPmean) of ≥ 25 mmHg at rest, based upon right heart catheterization measurement. According to the clinical and aetiological Dana Point classification PH is divided into five groups: Group I includes the rare form of pulmonary arterial hypertension (PAH), Group II PH with left heart disease, Group III PH associated with lung diseases and/or hypoxemia, Group IV PH owing to chronic thrombotic and/or embolic disease and Group V PH associated with miscellaneous other rare conditions. Diagnostic procedures in patients with suspected PH aim to determine the correct clinical classification and the functional and haemodynamic severity of the disease. Transthoracic echocardiography is the primary non invasive screening method and can provide a first classification of PH associated with left heart or shunt disease. Further elements employed in the differential diagnosis of PH are a precise anamnesis, imaging of the lung and a lung function test. If the classification of PH in the clinical Groups II or III is not evident, a ventilation/perfusion scan of the lung is recommend to detect segmental perfusion defects and allow or exclude the diagnosis of chronic thromboembolic pulmonary hypertension (CTEPH). If there is still no explanation of the PH aetiology, after exclusion of rare causes of PH Group V, PAH can be assumed. To prove the diagnosis, invasive measurement of pulmonary artery pressure by right heart catheterization is required.