The primary objectives of this study were to understand the origin of the Belize Barrier Reef and the sequence stratigraphy of the mixed siliciclastic-carbonate system. The data used consisted of 1,400 km of conventional multichannel seismic, 1,300 km of single-channel high resolution seismic, and information from nine wells. Conventional seismic shows elongated NNE-SSW highs and lows (Camels Basin, Camels Hump-Turneffe atoll, Gladden Basin, Glovers atoll-Lighthouse Island). The thrusted block of Camels Hump formed from buttressing of the Maya Mountains against the moving Caribbean plate during the Paleocene. Its load generated Camels Basin, whereas Gladden and Turneffe Basins formed as pull-aparts. The transtension produced the Turneffe and the Glovers-Lighthouse alignments whose tops as well as Camels Hump's were covered by carbonate platforms during the late Eocene/Oligocene. These carbonates were partially drowned in the early/middle Miocene. During the middle/late Miocene, tectonic enhancement of Camels Hump and Glovers highs triggered the collapse of their margins, shedding mass flow deposits. The late Pliocene/early Pleistocene sea-level fall moved the shoreline along the eastern flank of Camels Hump and in the northern Camels Basin where longshore currents redistributed the sediments. The Belize Barrier Reef became established on top of these lowstand siliciclastic coastal deposits in the middle of the Brunhes Epoch (about 0.45 Ma). Once the barrier reef was formed, it established the modern mixed siliciclastic-carbonate system. When sea-level dropped, about 120 m during the Last Glacial Maximum (18,000 years ago), the reef built during the previous interglacial highstand was karstified. The shelf lagoon became a fluvial plain drained by two incised valley systems. The northern fluvial system deposited a lowstand delta at the mouth of the English Cay Channel. This delta was partially reworked by longshore currents. The rise of sea-level slowed at about -65 to -70 m, 11,000 to 10,000 years ago (Younger Dryas) and is documented by a landward-stepped delta. As sea-level rise resumed, the incised valleys became filled with fluvial to estuarine sediments and, then, buried under marine marls. Flooding at about 7,000 years ago reactivated the reef.