"Inferring evolutionary relationships among a collection of organisms -- that is, their relationship to each other on the tree of life -- remains a central focus of much of evolutionary biology as these relationships provide the background for key hypotheses. For example, support for different hypotheses about early animal evolution are contingent upon the phylogenetic relationships among the earliest animal lineages. Within the last 20 years, the field of phylogenetics has grown rapidly, both in the quantity of data available for inference and in the number of methods available for phylogenetic estimation. The authors' first book, "Estimating Species Trees: Practical and Theoretical Aspects", published in 2010, gave an overview of the state of phylogenetic practice for analyzing data at the time, but much has changed since then. The goal of this book is to serve as an updated reference on current methods within the field. The book is organized in three sections, the first of which provides an overview of the analytical and methodological developments of species tree inference. Section two focuses on empirical inference. Section three explores various applications of species trees in evolutionary biology. The combination of theoretical and empirical approaches is meant to provide readers with a level of knowledge of both the advances and limitations of species-tree inference that can help researchers in applying the methods, while also inspiring future advances among those researchers with an interest in methodological development"--