The uniformity of rare-earth element (REE) patterns in clastic sedimentary rocks, due to the low solubility and short residence times of REE in the oceans, provides overall average upper crustal compositions for these elements. Effects of weathering, diagenesis, and metamorphism are minor. Local provenance is recorded in first-cycle sediments, but is rapidly erased with sediment maturity. The REE patterns in Archean sedimentary rocks indicate that the Archean crust was not highly evolved. It appears to have been dominated by basaltic and Na-rich granitic rocks (tonalites and trondhjemites). The REE patterns in Proterozoic and later sedimentary rocks indicate a major episodic break at the Archean/Proterozoic boundary. This is consistent with a change to a more differentiated upper crust, dominated by granodiorites, with negative Eu anomalies. These are inferred to result from intra-crustal melting, during which Eu is retained in a plagioclase-rich lower crust. Detailed descriptions of the change in REE patterns at the Archean/Proterozoic boundary are given for the Huronian (Canada) and Pine Creek Geosyncline (Australia) successions. Evidence from these successions, the Hamersley basin (Australia), and the Pongola (South Africa) sequence indicates that the change in upper crustal composition was not isochronous, but extended over a period from about 3.2 to 2.5 Ga ago. Abundance tables are given for the Proterozoic continental crust, upper and lower crusts, and the Archean crust. A model for continental crust evolution suggests that the evolution of the present crust began in the Archean and that most of the volume of the crust was formed from the mantle between 3.2 and 2.5 Ga. This was followed closely by intracrustal melting which produced the Proterozoic upper crust.