Everyone uses species. All human cultures, whether using science or not, name species. Species are the basic units for science, from ecosystems to model organisms. Yet, there are communication gaps between the scientists who name species, called taxonomists or systematists, and those who use species names—everyone else. This book opens the "black box" of species names, to explain the tricks of the name-makers to the name-users. Species are real, and have macroevolutionary meaning, and it follows that systematists use a broadly macroevolution-oriented approach in describing diversity. But scientific names are used by all areas of science, including many fields such as ecology that focus on timescales more dominated by microevolutionary processes. This book explores why different groups of scientists understand and use the names given to species in very different ways, and the consequences for measuring and understanding biodiversity.