Solar energetic particle (SEP) events are occasional bursts of high-energy particles from the Sun. Because of their episodic, highly variable, and (presently) unpredictable nature, these events are one of the primary constraints on the technological utilization of space and in the design and operation of space systems. New instruments on Wind and ACE, with geometry factors that are ~100 times larger than those of previous solar cycles, have yielded unprecedented observations of temporal evolution in composition and spectra over a wind range of energies and species. These new results address some of the key physics that governs SEP production. Of particular importance in very large SEP events are transport effects due to proton-generated Alfv¿n waves and the evolving nature of the coronal mass ejection driven shock. ¿ 2001 American Geophysical Union