An interlocking ladder of relative gas-phase acidities of a large number of very strong CH (substituted phenylmalononitriles, 2,4,6-(CF3SO2)(3)C6H2CH3, CF3SO2- and FSO2-substituted methanes, TNT, etc.), NH (bis(perfluoroalkyl)sulfonyl imides, 2,4,6-(CF3SO2)(3)C6H2NH2, etc.), OH (triflic acid, picric acid, 2,4,6-(CF3SO2)(3)C6H2OH, CH3SO3H, etc.) and SH (CF3COSH) Bronsted acids has been obtained using the pulsed FT ion cyclotron resonance (ICR) equilibrium constant method. The new intrinsic acidity scale covers a wide range from (CF3)(2)NH (Delta G(acid) = 324.3 kcal/mol) to (C4F9SO2)(2)NH (Delta G(acid) = 284.1 kcal/mol) and is anchored to the thermodynamic Delta G(acid) value (318.1 kcal/mol) of HBr. In several cases, the gas-phase acidity of compounds which make up the scale exceeds the acidity of such traditionally strong mineral acids as HCl, HBr, HI, or H2SO4 by more than 30 powers of 10. The roles of the acidity sites (CH, NH, OH, SH) and the structural factors (i) field/inductive effects (F), (ii) pi-electron-acceptor resonance effects (R), and (iii) substituent polarizability (P) effects on increasing the gas-phase acidity of Bronsted acids are discussed. The effects of multiple substitution in families of Bronsted acids have been measured and discussed. The strong and extensive chains of conjugation in the resonance-stabilized planar conjugate anion of (p-nitrophenyl)malononitrile lead to the same gas-phase CH acidity (Delta G(acid) = 299.5 kcal/mol) as for OH superacid CF3SO3H. A single para substituent in aniline has been found that exerts such a powerful "electron-withdrawing" effect that this aniline has a stronger gas-phase acidity than CH3SO3H. The substituent is S(O)(=NSO2CF3)CF3, one of the family of Yagupolskii superacceptor substituents that is generated by replacing =O by =NSO2CF3 at a bonded S, P, or I (including in addition to the above -S(=NSO2CF3)(2)CF3, -P(=NSO2CF3)(C3F7)(2) and -I=NSO2CF3). Perfluoroaromatic acids have been identified as well-behaved compounds for gas-phase acidity determinations. Their moderately strong inherent acidifying effects are illustrated by the fact that a Delta G(acid) value of 302 +/- 1 kcal/mol applies to all of the following : (4-C5F4N)(2)CHCN, (p-CF3C6F4)(2)CHCN, beta-C10F7CH(CN)(2), and (CF3SO2)(2)CH2.