Concentrations of the cosmogenic isotope 10Be have been measured in more than 1350 samples from the Greenland Ice Core Project (GRIP) ice core drilled at Summit, Greenland. Although a dust-associated component of 10Be retained by 0.45 μm filters in some of the samples complicates the interpretations, the results confirm that the first-order origin of 10Be concentration variations is changes in precipitation rate associated with different climate regimes. This effect is seen not only between glacial and interglacial periods, but also during the shorter Dansgaard-Oeschger interstadials. By contrast, the 10Be data do not support the interpretation of rapidly varying accumulation (i.e., climate) during the last interglacial. They can, however, be used to help place limits on the origin of the ice in these events. After taking into account variable snow accumulation effects, variations in the 10Be flux are observed, probably caused by solar and geomagnetic modulation, but possibly also by primary cosmic ray variations. The most dramatic is a 10Be peak ~40,000 years ago, similar to that found in the Vostok ice core, thus permitting a very precise correlation between climate records from Arctic and Antarctic ice cores. The 36Cl/10Be ratio (considering either total or only ice-associated 10Be) shows significant variability over the whole core depth, thus confirming the difficulty in using this parameter for dating ice cores. ¿ 1997 American Geophysical Union