Publisher Summary The imidazole nucleus is important in biological processes and the applications of imidazoles as pharmaceuticals and in industrial processes is growing. The chapter aims to survey developments in imidazole chemistry to mid-1979, limiting the discussion to the simple heteroaromatic ring (condensed or reduced imidazoles are not covered). Formation of various types of imidazole ring with different bond orientation is discussed in the chapter. Formation from other heterocycles such as five membered heterocycles, ring expansion and contraction are also discussed. The chapter elaborates physical properties that include dipole moments, acid and basic strength, ultraviolet and visible spectra, infrared spectra, NMR spectra, ESR spectra, mass spectrometry, quantum-mechanical studies, and Hammett studies. The chapter also discusses its chemical properties such as structure ant tautomerism, electrophile substitution reaction at ring nitrogen and carbon atoms, nucleophilic substitution reaction, photochemical reactions, thermal reactions, and reaction of substituent groups.