There are several ways to estimate past sea surface temperature (SST) and other paleoceanographic parameters using fossil plankton. Oxygen isotope measurements of delta18O in foraminiferal tests provide estimates of sea-water delta18O at the time the carbonate was secreted by the organism. These values can be used to estimate ambient water temperature at the time of secretion as long as assumptions are made about vital effects and the salinity of the sea water (Emiliani 1955, 1966, 1972). Due to uncertainties in ice volume history—in the Neogene primarily the state of Antarctic ice—isotopic estimates of temperature must be viewed with some degree of uncertainty. Paleoceanographers have also used the distribution of fossil foraminifers to estimate past SST. Whether based on qualitative or quantitative techniques, these estimates depend upon a thorough knowledge of the modern distribution of taxa in the world ocean, and the assumption that specific taxa have not changed ecological tolerances over time. These ideas led Imbrie and Kipp (1971) and Kipp (1976) to develop the transfer function technique which was the foundation of the Climate, Long Range Investigation and Mapping (CLIMAP) Project (CLIMAP 1976, 1981, 1984). As part of the Pliocene Research, Interpretation, and Synoptic Mapping (PRISM) Project, various statistical methods have been developed to transform Pliocene faunal census data into estimates of physical oceanographic parameters such as sea surface temperature (SST) and salinity (Dowsett and Poore 1990, Cronin and Dowsett 1990, Dowsett 1991). This paper focuses on the Modern Analog Technique (MAT) and its application to pre-Pleistocene planktonic foraminifer assemblages. The MAT method has been discussed in detail by Hutson (1979), Prell (1985), and Anderson et al. (1989) who applied it to late Pleistocene applications planktonic foraminiferal data, but there are relatively few applications (Dowsett 1996, Andersson 1997) available to illustrate the technique’s use with pre-Pleistocene samples. In this paper we review the methodology and apply the MAT technique to Pliocene sediments in the North Pacific to evaluate its usefulness for pre-Pleistocene SST estimation.