Over 90% of prostate cancers over-express prostate specific membrane antigen (PSMA) and these tumor cells may be accurately targeted for diagnosis by Ga-68-PSMA-positron emission tomography/computed tomography (Ga-68-PSMA-PET/CT) imaging. This novel molecular imaging modality appears clinically to have superseded CT, and appears superior to MR imaging, for the detection of metastatic disease. Ga-68-PSMA PET/CT has the ability to reliably stage prostate cancer at presentation and can help inform an optimal treatment approach. Novel diagnostic applications of Ga-68-PSMA PET/CT include guiding biopsy to improve sampling accuracy, and guiding surgery and radiotherapy. In addition to facilitating the management of metastatic castrate resistant prostate cancer (mCRPC), Ga-68-PSMA can select patients who may benefit from targeted systemic radionuclide therapy. Ga-68-PSMA is the diagnostic positron-emitting theranostic pair with the beta emitter Lutetium-177 PSMA (Lu-177-PSMA) and alpha-emitter Actinium-225 PSMA (Ac-225-PSMA) which can both be used to treat PSMA-avid metastases of prostate cancer in the molecular tumor-targeted approach of theranostic nuclear oncology.