Taxonomy is the theory and practice of identifying animals. In fact, taxonomy deals with the principles involved in the study of classification of organisms. It is the functional science which deals with identification, nomenclature and classification of different kinds of organisms all over the world. Taxonomy is the most important branch of systematic and thus systematics is a broader area than taxonomy. The classical taxonomy is based on observable morphological characters with normal individuals considered to be expression of the same while their variations are believed to be imperfect expressions. Classical taxonomy originated with Plato followed by Aristotle (Father of Zoology), Theophrastus (Father of Botany) up to Linnaeus (Father of Taxonomy) and his contemporaries. Systematics is the key to understand fascinating biodiversity around us. Systematics benefits the human beings by providing the fundamental knowledge about the sustainable resource management, environmental protection, and landscape preservation to food security. Systematic biology provides the skill to make policies for successful implementation of preservation and management of our biodiversity, which is critical to have long term quality of life for us as well as to our nature. Biologists and taxonomists have made many attempts to define species, beginning from morphology and moving towards genetics. Early taxonomists such as Linnaeus had no option but to describe what they saw: this was later formalised as the typological or morphological species concept. The present book provides a comprehensive account of the general principles and modern trends in the taxonomy of animals.