Gamma cameras play an important role in nuclear medicine by detecting gamma radiation emitted by radiopharmaceuticals. This chapter focuses on the key principles, technologies, and clinical applications of gamma cameras and single photon emission computed tomography (SPECT), particularly within hybrid imaging systems. Understanding the technology behind the gamma camera is essential for optimizing acquisition techniques. The collimators, scintillation crystal, and photomultiplier tubes play a crucial role in converting gamma photons into images. SPECT utilizes gamma camera technology, originally developed for planar imaging, to produce 3D tomographic images. This chapter explores the fundamentals of SPECT image acquisition and the integration of SPECT with CT in hybrid systems. Hybrid imaging has significantly enhanced diagnostic capabilities by combining functional and anatomical data, making a substantial impact on clinical nuclear medicine, particularly in oncology, cardiology, and neurology. Finally, the chapter addresses the challenges and limitations of SPECT/CT and its common clinical applications.