We study choanoflagellates and the evolution of multicellular animals from their unicellular ancestors. The origin of animals represents one of the pivotal transitions in life's history, and one of its greatest unsolved mysteries. While the fossil record remains silent regarding the rise of multicellularity, the genetic and developmental foundations of animal origins may be deduced from shared elements among extant animals and their protozoan relatives, the choanoflagellates. To better understand the origin and evolution of animals, our goals are to [1] determine the minimal genomic complexity of the common ancestor of animals, [2] elucidate the ancestral functions of genes required for multicellular development, [3] characterize choanoflagellate cell and developmental biology, and [4] test the hypothesis that the emergence of multicellular animals stemmed, in part, from the evolution of new modes of gene regulation.