Medial branch blocks are used to test if the pain stems from a zygapophysial joint because the medial branch innervates the joint. If the pain is not relieved after a medial branch block, the target nerve cannot be regarded as mediating the pain; this means the zygapophysial joint is not the pain source. If the answer is positive, the pain source is identified and a good chance of obtaining pain relief after radiofrequency neurotomy is predicted. The fundamental indication for medial branch blocks is the desire to know if the zygapophysial joints are the pain source. No clinical test exists to identify a zygapophysial joint as pain source. Because the singular reason for performing diagnostic medial branch blocks is to obtain information, the evaluation of the patient’s response is essential. A strong accuracy of facet joint nerve blocks in the diagnosis of lumbar and cervical facet joint pain can be achieved. Diagnostic lumbar facet joint nerve blocks are recommended in patients with suspected facet joint pain. Conflicting results of different treatment modalities are discussed: the degree of relief that should occur after medial branch blocks remains contentious. Medial branch blocks are a diagnostic tool. However, there are studies giving a strong recommendation for the use of therapeutic cervical and lumbar facet joint nerve blocks for the treatment of chronic facet joint pain. The evidence for intra-articular injections seems to be poor. Computed tomography (CT) guidance is not supported by guidelines.