This chapter explores different aspects relating to the diversity of the dinoflagellates studied during two consecutive seasonal cycles (August 2004 - July 2006) along the beach surf-zone systems of São Paulo State, Brazil. We first provide the broad context in which dinoflagellate assemblages are inserted within the total phytoplankton, diatom-dominated dynamics in relation to physical forcings, in particular, to wave climate. Next, we discuss spatiotemporal trends in the dinoflagellate assemblage per se, making use of several biodiversity parameters. The chapter also focus on novel and interesting armored species, as well as some selected unarmored taxa, within the context of what is known about their ecology and biogeography. Monthly dinoflagellate diversity for the whole study area varied between 13 and 51 taxa. The strongest signal in terms of frequencies of occurrence and relative abundance was detected in more protected beaches of the northern sector. The highest biodiversity, however, was most often detected at beaches of intermediate wave height, not exclusive to the northern sector, and included representatives of a wide variety of morpho-functional groups from high surface-to-volume, fast-growing colonist species to slow-growing, stress-tolerant species. Our inventory lists 135 taxa distributed in 37 genera. New records for Brazilian waters consist of 17 species, including three genera (Diplopelta parva, Lissodinium cf. taylorii, and Leptodiscus medusoides). The first two, together with the majority of the first citations of armored dinoflagellates for the coast of Brazil, were detected as part of the beach-surf zone floras; the third is an unarmored species opportunistically detected in the São Sebastião Channel. Except for the genus Tripos, for which 45 species are listed, our perception of the dinoflagellate diversity in this region is still underestimated. Future studies will hopefully implement analysis of live material, including the establishment of cultures, foster sampling from bottom sediments, epiphytic communities, and the water column further away from the coastline, as well as make use of molecular tools to further reveal cryptic diversity.