Science, philosophy of science, and metaphysics have long been concerned with the question of how order, stability, and novelty are possible and how they happen. How can order come out of disorder? This book introduces a new account, contextual emergence, seeking to answer these questions. The authors offer an alternative picture of the world with an alternative account of how novelty and order arise, and how both are possible. Contextual emergence is grounded primarily in the sciences as opposed to logic or metaphysics. It is both an explanatory and ontological account of emergence that gets beyond the impasse between "weak" and "strong" emergence in the emergence debates. It challenges the "foundationalist" or hierarchical picture of reality and emphasizes the ontological and explanatory fundamentality of multiscale stability conditions and their contextual constraints, often operating globally over interconnected, interdependent, and interacting entities and their multiscale relations. It also focuses on the conditions that make the existence, stability, and persistence of emergent systems and their states and observables possible. These conditions and constraints are irreducibly multiscale relations, so it is not surprising that scientific explanation is often multiscale. Such multiscale conditions act as gatekeepers for systems to access modal possibilities (e.g., reducing or enhancing a system's degrees of freedom). Using examples from across the sciences, ranging from physics to biology to neuroscience and beyond, this book demonstrates that there is an empirically well-grounded, viable alternative to ontological reductionism coupled with explanatory anti-reductionism (weak emergence) and ontological disunity coupled with the impossibility of robust scientific explanation (strong emergence). Central metaphysics of science concerns are also addressed. Emergence in Context: A Treatise in Twenty-First Century Natural Philosophy is written primarily for philosophers of science, but also professional scientists from multiple disciplines who are interested in emergence and particularly in the metaphysics of science.