Traditionally, archaeologists have used l4C dating primarily as a postexcavation analytical tool to establish the age of features, strata, or assemblages. In coastal zones and other environments around the world, however, thousands of archaeological sites are rapidly eroding or endangered by other destructive processes. We believe archaeologists should expand their use of l4C dating, systematically incorporating it into surveys in coastal, lacustrine, riverine, and other environments where erosional exposures often provide access to extensive stratigraphic profiles. With examples from the Pacific Coast of North América, we show how widespread l4C dating of sites during surveys can be used to help manage archaeological sites more effectively and identify significant patterns of paleoenvironmental change, site survival, settlement and demography, technology, and social organization. Without more widespread application of such techniques, and a reallocation of research and cultural resource management funds, thousands of sites will be lost before even the most basic information about their age and contents is known.