This book offers a comprehensive reflection on the existential condition of the 21st century. A visionary introduction to existential posthumanism, it takes the form of eight meditations of posthuman self-inquiry. Existential posthumanism embraces the question 'Who am I?' in relation to: 'Where, When, and Why are We?'. This journey of self-discovery engages with a wide range of knowledge and expertise - from ancient paths of wisdom to the latest developments in science and biotechnologies; from Paleolithic times to the futures of radical life extension. The book declutters the habit of being human: as individuals, as societies, as a species. Letting go of the need for anthropocentric mastery and species-specific ambitions, the reader emerges regenerated. Being posthuman, in the 21st century, entails awareness of inter-being: from our symbiotic co-evolutions to the rights of Nature; from the geological time of the Anthropocene to the rise of Big Data and artificial intelligence. In ecology, biology, technology and ontology, the manifold paths of posthuman self-realization will reveal that we are all co-creators in the existential unfolding: our lives are our ultimate works of art. The Art of Being Posthuman is a self-help guide to navigate our brave new world.