The purpose of this symposium is to bring together researchers across different disciplines with a shared interest in studying the origins and consequences of variability in biological systems, ranging from stochastic molecular fluctuations to emerging cell population-level phenomena. The symposium will highlight the important role that single-cell approaches now have across the whole life sciences, be it in studying the dynamics of a molecular system in tissue culture cells or developing organisms, in understanding cell fate decisions during stem cell differentiation, in interpreting results from large-scale perturbations, or in mapping the cellular heterogeneity underlying drug resistance in cancer.