Pyridyl- and imidazolylphosphines accelerate anti-Markovnikov alkyne hydration and alkene isomerization and deuteration by factors of 1000 to more than 10000. Evidence for proton transfer and hydrogen bonding in catalytic intermediates comes from computational, mechanistic, and structural studies. Related concepts are being applied to a novel class of protic N-heterocyclic carbene complexes which feature an unusual NH group.