The idea there is a “balance of nature” was a staple of the schools of natural philosophy from which biology emerged. Not until the second half of the twentieth century was the concept of a balance of nature rigorously characterized as ecological stability, and the metaphysical speculations about its cause superseded with scientific hypotheses about its basis. But significant uncertainty and controversy exists about what features of an ecological system’s dynamics should be considered its stability and thus no consensus has emerged about how ecological stability should be defined. Instead, ecologists have employed a confusing multitude of different terms to attempt to capture apparent stability properties, e.g., constancy, persistence, resilience, resistance, robustness, tolerance. This chapter diagnoses and resolves the underlying lack of conceptual clarity about ecological stability. It presents a comprehensive account of stability as a three-fold concept that crucially depends on two reference specifications. The account clarifies the concepts ecologists have used that are defensible, their interrelationships, and their potential relationships with other biological properties. Besides providing insights about how problematic scientific concepts should be characterized, the idea that ecological stability is a conceptually confused concept is also criticized.