Benzhydrylium ions (Ar2CH+) and structurally related quinone methides are employed as reference electrophiles for comparing the nucleophilicities of a large variety of compounds, e.g., alkenes, arenes, alkynes, allylsilanes, allylstannanes, enol ethers, enamines, diazo compounds, carbanions, transition-metal π-complexes, hydride donors, phosphanes, amines, alkoxides, etc., using the correlation equation log k (20 °C) = s(N + E), where s and N are nucleophile-dependent parameters and E is an electrophilicity parameter. The same equation was employed to derive the electrophilicity parameter E for different types of carbocations, cationic transition-metal π-complexes, typical Michael acceptors, and electron-deficient arenes. The E, N, and s parameters thus obtained can be used for predicting rates and selectivities of polar organic reactions.