Earth has entered the Anthropocene: a new geological period. From genes to ecosystems, the entire biological spectrum is changing faster and in different ways from any time in the past, driven by human-induced exploitation, habitat degradation, pollution and climate change, with substantial flow-on consequences for human society. One of the most striking effects has been dramatic changes in the species composition of ecological communities across the globe resulting in novel communities living in novel climates, residing in novel ecosystems and driving novel human and ecosystem interactions. The concept of ecological novelty was originally described as ‘…modified natural systems that have crossed irreversible socio-ecological thresholds due to human-induced environmental change’ (Backstrom et al. 2018), but the concept has suffered from the lack of a quantitative framework to push it forward into real-world applications useful at the scale of ecosystem management. However, a theoretical, quantitative and predictive foundation for ecological novelty is beginning to emerge, drawing on data and principles from conservation biology and palaeoecology. Here, we outline five universal components of quantitative novelty, combining them into a single, high-level conceptual framework. This framework can be flexibly applied to a range of scales and research and management foci. We illustrate this framework using examples of time-series data from marine plankton, coral reef and terrestrial plant communities. Application of a consistent framework in describing ecosystem novelty will enhance our ability to aggregate and compare findings among ecosystems, sites, and time scales, driving future research and delivering benefits to real-world ecological management and protection.