Polymeric micelles provide a platform that can be carefully tuned for drug delivery. The nano-scale aggregates form spontaneously in aqueous solution and can be used to overcome drug insolubility and increase circulation half life. Self-assembled polymeric micelles are dynamic in nature; thermodynamics defines how the system acts as micelles approach equilibrium, while kinetics characterizes the system's behavior over time. In this review, we discuss factors that affect the stability of self-assembled polymeric micelle systems for drug delivery and methods used to study stability. Considerations of polymer composition, drug encapsulation, and environmental conditions influence polymeric micelle stability. Ultimately, we emphasize the importance of investigating micelle systems in physiologically relevant media to improve therapeutic efficacy and reduce systemic toxicity in clinical applications. (C) 2012 Elsevier Ltd. All rights reserved.