Allosteric modulation of G protein-coupled receptors (GPCRs) is nowadays a hot topic in medicinal chemistry. Allosteric modulators, i.e., compounds which bind in a receptor site topologically distinct from orthosteric sites, exhibit a number of advantages. They are more selective, safer and display a ceiling effect which prevents overdosing. Allosteric modulators of dopamine D2 receptor are potential drugs against a number of psychiatric and neurological diseases, such as schizophrenia and Parkinson’s disease. In this review, an insightful summary of current research on D2 receptor modulators is presented, ranging from their pharmacology and structural aspects of ligand-receptor interactions to their synthesis.