The story of the discovery, investigation, and eventual correct formulation of fulminic acid, HCNO, extends over a period of 200 years and reflects uniquely, in its many stages, the evolution of organic chemistry from post-alchemistic times to the age of wave mechanics. Fulminic acid was discovered in 1800 when E. Howard serendipitously prepared its highly explosive mercury and silver salts. The determination of its structure presented unusual difficulties and taxed the ingenuity of leading chemists of successive generations. Their work generated a procession of proposed and discarded formulations that was only finally ended in the 1960s with the recognition of fulminic acid as the mesomeric structureand hence with its identification as the parent compound of the important class of the nitrile N-oxides. Recently fulminic acid and several of its isotopomers have been subjected to the most searching spectroscopic investigations and ab initio computations, by which its molecular dimensions and geometry, and its "quasi-linear" structure have been revealed. In technology, mercury fulminate occupied for nearly a century a uniquely important position as the only available practical detonator for every kind of conventional explosive.