The measurement of the lifetimes of excited states of molecules by picosecond time-resolved fluorescence methods is discussed. Attention is focused on the methods that involve the use of mode-locked solid-state and dye lasers as excitation sources. Time-correlated photon counting and direct recording using streak cameras are the diagnostic methods that have proved most useful at times of less than 1 ns. The second section of the report outlines some work carried out at the Center for Fast Kinetics Research in which the variation of fluorescence lifetime of some xanthene dyes with changes in their environment has been used to deduce information on the strengths of hydrogen bonds therein. Both neat organic solvents and aqueous surfactant micelles have been employed.