This paper explores the relative importance of deterministic and stochastic processes in shaping community structure and biodiversity patterns across ecological and biogeographic scales. It emphasizes the need to disentangle the roles of ecological niches and stochastic processes in generating site-to-site variation in species composition (β-diversity) along gradients of disturbance, productivity, and biotic interactions, as well as among regions with different regional species pool sizes. The authors propose a framework that uses null-model approaches to distinguish deterministic processes (e.g., niche-based selection) from stochastic processes (e.g., ecological drift, random colonization and extinction) by accounting for local and regional factors that inherently create stochastic turnover. They argue that both deterministic and stochastic processes are simultaneously at play in ecological communities, and that the relative importance of each can vary across scales. The paper highlights the importance of considering how deterministic processes, such as niche-based selection, interact with stochastic processes, and how these interactions can influence patterns of biodiversity. It also discusses the challenges of distinguishing between deterministic and stochastic processes, particularly when stochasticity is high, and emphasizes the need for careful analysis of β-diversity patterns to disentangle these processes. The authors illustrate these concepts using examples from ecological studies, including those involving pond communities, and emphasize the importance of considering spatial and environmental factors in understanding community assembly. The paper concludes that a synthesis of deterministic and stochastic processes is necessary to fully understand the mechanisms underlying biodiversity patterns in ecological communities.This paper explores the relative importance of deterministic and stochastic processes in shaping community structure and biodiversity patterns across ecological and biogeographic scales. It emphasizes the need to disentangle the roles of ecological niches and stochastic processes in generating site-to-site variation in species composition (β-diversity) along gradients of disturbance, productivity, and biotic interactions, as well as among regions with different regional species pool sizes. The authors propose a framework that uses null-model approaches to distinguish deterministic processes (e.g., niche-based selection) from stochastic processes (e.g., ecological drift, random colonization and extinction) by accounting for local and regional factors that inherently create stochastic turnover. They argue that both deterministic and stochastic processes are simultaneously at play in ecological communities, and that the relative importance of each can vary across scales. The paper highlights the importance of considering how deterministic processes, such as niche-based selection, interact with stochastic processes, and how these interactions can influence patterns of biodiversity. It also discusses the challenges of distinguishing between deterministic and stochastic processes, particularly when stochasticity is high, and emphasizes the need for careful analysis of β-diversity patterns to disentangle these processes. The authors illustrate these concepts using examples from ecological studies, including those involving pond communities, and emphasize the importance of considering spatial and environmental factors in understanding community assembly. The paper concludes that a synthesis of deterministic and stochastic processes is necessary to fully understand the mechanisms underlying biodiversity patterns in ecological communities.