Since the discovery of medium-chain fatty acids as GPR84 ligands, significant advancements have been made in the development of GPR84 agonists and antagonists. Most agonists have lipid-like structures except for 3,3'-diindolylmethane (DIM), which acts as an allosteric agonist. GPR84 activation in macrophages leads to increased cytokine secretion, chemotaxis, and phagocytosis, revealing the proinflammatory role of GPR84 associated with various inflammatory responses. Three GPR84 antagonists (S)-2-((1,4-dioxan-2-yl)methoxy)-9-(cyclopropylethynyl)-6,7-dihydro-4H-pyrimido[6,1-a]isoquinolin-4-one (GLPG1205), sodium 2-(3-pentylphenyl)acetate (PBI-4050), and sodium 2-(3,5-dipentylphenyl)acetate (PBI-4547) have displayed therapeutic effects in animal models of several inflammatory and fibrotic diseases and are being evaluated in clinical studies. Although GLPG1205 has failed in a clinical trial for ulcerative colitis, it is undergoing another phase II clinical study for idiopathic pulmonary fibrosis. Further studies are needed to resolve the GPR84 structure, identify more endogenous ligands, elucidate their physiological and pathological roles, and fulfill the therapeutic potential of GPR84 antagonists and agonists.