Setophaga cerulea (Cerulean Warbler) is one of the fastest declining avian species in the United States, and its conservation has been hampered by a lack of basic biological information. Here we describe basic breeding biology and behavior and report incidental observations of scientific interest from three years of research on Cerulean Warblers in the Cumberland Mountains of eastern Tennessee. We located and monitored 241 nests and banded 83 Cerulean Warblers from 2008–2010. We documented mating strategies, timing and plasticity of reproduction, details of nest construction and maintenance, parental behavior, predation of juveniles, post-fledging behavior, interspecific interactions, female weight, and a longevity record. Many of these observations have not been formally recorded and add new dimensions to our understanding of Cerulean Warbler biology, ecology, and life history.