Calibration curves spanning several millennia are now available in this special issue ofRadiocarbon. These curves, nearly all derived from the14C age determinations of wood samples, are to be used for the age conversion of samples that were formed through use of atmospheric CO2. When samples are formed in reservoirs (eg, lakes and oceans) that differ in specific14C content from the atmosphere, an age adjustment is needed because a conventional14C age, although taking into account14C (and13C) fractionation, does not correct for the difference in specific14C activity (Stuiver & Polach, 1977). The14C ages of samples grown in these environments are too old, and a reservoir age correction has to be applied. This phenomenon has been referred to as the reservoir effect (Stuiver & Polach, 1977).