The hierarchical approach to evolution, emerged since the 1980s at the crossroads of paleobiology, genetics, and developmental biology, has grown into a unifying perspective on the natural world and today offers an operational framework to understand the way complex biological systems work and evolve. This volume, written by a multidisciplinary group of authoritative contributors, provides an integrated, comprehensive, cutting-edge introduction to the hierarchy theory of evolution. Part 1 clarifies the kinds of hierarchies, levels and relations that the hierarchical approach has outlined over decades of theoretical work. These foundational, terminological and epistemological issues lead to Part 2, devoted to exploring several evolutionary scales and their interactions, from genes and genomes, to organismal phenotype and development, to natural selection and individuality at multiple scales, to the evolving biosphere. Part 3 illustrates theoretically and empirically the interactions between the two main hierarchies of the theory – the ecological or economic hierarchy and the evolutionary or genealogical hierarchy – especially at macroevolutionary scale. The dual hierarchical framework re-conceptualizes pivotal notions such as speciation, niche, stasis and community, and provides insights into the macroevolutionary role of humanity. The editors, including Niles Eldredge one of the founders of hierarchy theory, guide the reader with introductions and linking sections to understand the internal logic and the historical importance of the hierarchical perspective, and its advantages compared to other unifying proposals in evolutionary biology. The hierarchical evolutionary theory is to be studied as a candidate research programme where different approaches and models can find their reciprocal relevance.