Mass balance calculations based on a data compilation lead us to estimate a δ18O value of 8.9 ¿ 0.7? for the continental crust. This isotopic composition is the product of two competing processes, namely, the erosion and growth of continental masses. Erosion tends to enrich the continental crust in 18O through low-temperature isotopic exchange with the hydrosphere, whereas continental growth maintains the composition of the crust close to its mantle-derived precursor (δ18O = 5.7?). Box modeling of the oxygen isotope exchange between the continents, mantle, and seawater leads us to calculate a flux of subducted sediments averaged over the Earth's history of 0.4 km3 yr-1, significantly lower than most other recent estimates.