Abstract: A vexing issue in evolutionary biology has been the reaching of a stable Animal Tree of Life. The use of numerical methods to study morphology in a systematic context and the advent of molecular data in the form of target-gene approaches have revitalized the field of animal phylogenetics and have contributed to many rearrangements in the Tree of Life. More recently, the study of full genomes or significant fractions through Expressed Sequence Tags (ESTs) have led to unprecedented amounts of molecular data available to study relationships. The use of these data in an integrative fashion with morphology and development has yielded stable hypotheses in what we now considered a modern Animal Tree of Life.