This lecture will briefly summarizes the state-of-the art developments in radiation detectors used in Nuclear Medicine instrumentation regarding various detector technologies and designs of different geometries. Preclinical “low cost” imaging systems, very high-resolution research applications (including small-animal imaging), and MR combined systems will also be discussed. Options of new bright scintillators and photodetectors will be mentioned, including co-doped and mixed scintillator materials as well as discrete silicon photomultiplier arrays (SiPMs). Finally, it will be analyzed how the crucial parameters (energy, spatial and timing resolution, sensitivity and injection dose) improved with whole body geometry and time of flight (ToF) techniques.