This chapter gives an overview of single photon emission computed tomography in the evaluation of lung diseases. Single photon emission computed tomography is the recommended scintigraphic technique for the diagnosis of pulmonary embolism (PE) and many other disorders that affect lung function. This chapter also covers the Ventilation/perfusion SPECT and pulmonary embolism, imaging protocols, basic principles of pulmonary embolism diagnosis with V/P SPECT, reporting findings, criteria for acute pulmonary embolism, chronic pulmonary embolism, role of ventilation SPECT in diagnosis of other lung diseases, V/P SPECT versus MDCT and clinical use of hybrid V/P SPECT/CT. To take full advantage of the V/P SPECT potential, it is crucial to apply an optimal protocol for a single session imaging of both ventilation and perfusion using low nuclide activities.