The elucidation of detailed mechanisms of ultrafast events that occur in reactions has been made possible by recent advances in spectroscopy techniques that use ultrashort laser pulse generation. Ultrashort laser pulses (100 femtoseconds duration, 1 fs = 10 - 1 5 s) allow to initiate selective photochemical processes (single charge transfer for instance) and to obtain unique informations on the dynamics of primary steps of radical reactions involving ultrafast electron or proton transfer: transient electronic relaxation, formation of solvation cage, encounter pair formation, ion-molecule reaction. Recent investigations on the femtochemistry of neat liquid water and ionic aqueous solutions are reviewed and discussed.