Publisher Summary This chapter discusses the 3 H -pyrazoles that have been isolated or characterized spectroscopically. 3 H -Pyrazoles can be synthesized from (1) diazo compounds and alkynes, (2) diazo compounds and alkenes bearing suitable leaving groups, (3) diazo compounds by other intermolecular processes, (4) cyclization of vinyl diazo compounds, (5) pyrazolines, (6) miscellaneous methods (from 4-bromo-4 H -pyrazoles and tetrazolopyrimidine), (7) N -oxides and N , N’ -dioxides, and (8) N -Ylides. The chapter describes the structure (X-ray crystallography and tautomerism) and spectroscopic properties (ultraviolet spectra, infrared spectra, 1 H-NMR spectra, 13 C-NMR spectra, 19 F-NMR spectra, mass spectra, and photoelectron spectra) of 3 H -pyrazoles. Thermal reactions formally involving no other species, photochemical reactions formally involving no other species, reactions of ring atoms with electrophiles, reactions of ring atoms with nucleophiles, reactions with cyclic transition states, and reactions of ring substituents outlined in the chapter describe the chemical properties of 3 H -pyrazoles.