It is commonly agreed that a self-adaptive software system is one that can modify itself at run-time due to changes in the system, its requirements, or the environment in which it is deployed. A cursory review of the software engineering literature attests to the wide spectrum of software systems that are described as self-adaptive. The way self-adaptation is conceived depends on various aspects, such as the users’ requirements, the particular properties of a system, and the characteristics of the environment. In this paper, we propose a classification of modeling dimensions for self-adaptive software systems. Each modeling dimension describes a particular facet of the system that is relevant to self-adaptation. The modeling dimensions provide the engineers with a common set of vocabulary for specifying the self-adaptive properties under consideration and select suitable solutions. We illustrate how the modeling dimensions apply to several application scenarios.