Noise is widely regarded as a residual category--the unexplained variance in a linear model or the random disturbance of a predictable pattern. Accordingly, formal models often impose the simplifying assumption that the world is noise-free and social dynamics are deterministic. Where noise is assigned causal importance, it is often assumed to be a source of inefficiency, unpredictability, or heterogeneity. We review recent sociological studies that are noteworthy for demonstrating the theoretical importance of noise for understanding the dynamics of a complex system. Contrary to widely held assumptions, these studies identify conditions in which noise can increase efficiency and predictability and reduce diversity. We conclude with a methodological warning that deterministic assumptions are not an innocent simplification.