Although sea-level fluctuations are known to have occurred throughout the earth's history, their global synchroneity, amplitude, and rate are still largely unknown. A better understanding of global changes in sea level is contingent upon coverage in a variety of tectonic and sedimentary settings, such as the deep sea, carbonate platforms and atolls, and continental margins. The primary objective of Leg 166 will be to address fundamental questions regarding sea level. To attain this objective, five sites in the Straits of Florida will be drilled during Leg 166, completing a transect through prograding carbonate sequences formed in response to sea-level fluctuations along the western margin of the Great Bahama Bank. Two boreholes drilled previously on the western Great Bahama Bank as part of the Bahamas Drilling Project represent the shallow-water sites of the transect. The primary goal of the transect is to document the platform-margin record of the Neogene-Holocene sea-level changes by determining the ages of the major unconformities and to compare the timing of these unconformities with ages predicted from the oxygen isotopic record of glacio-eustasy. Core borings along the complete transect will document the facies variations associated with oscillations of sea level and, thus, the sedimentary response of the carbonate environment to sea-level changes. The correlation between the two independent records of sealevel changes, sequence stratigraphy and oxygen isotope proxy, has the potential to evaluate rate and amplitude of eustatic vs. relative sea-level changes and to establish a causal link between glacio-eustasy and the stratigraphic pattern. Leg 166 also will core a number of holes through the sediments on the upper slope to measure the composition of the recharged waters retained in the sediment to assess rate and flow mechanisms through the bank. One of the distal sites of the transect will be deepened to determine the onset of the Florida Current, acquire a low-latitude record of the Paleogene "Doubthouse" and its transition into the Neogene "Icehouse," potentially sample the Cretaceous/Tertiary (K/T) boundary, and core the middle Cretaceous sequence boundary to assess the cause of the platform demise in the middle Cretaceous.