Requirements of software systems tend to change over time. The speed of this tendency depends on the application domain the software system under consideration belongs to. If we consider novel contexts such as pervasive systems and systems supporting dynamic B2B interaction, requirements change so fast that the research community is studying how to build systems that are able to self-adapt on the fly to some of these changes. When this happens, the system does not need to undergo through a new development cycle thus increasing its availability and, to a certain extent, its robustness. So far, the research in the area of self-adaptive systems has been focusing on the definition of the mechanisms for supporting self-adaptation. We argue that what is missing now is a structured and robust design process associated to these mechanisms. This design process should include a Requirement Engineering (RE) phase that somewhat differs from the traditional one. However, the identification of requirements for adaptation requires a good knowledge of the context in which the system will be executed. In this work, we consider the modeling of such context as part of the RE phase and we particularly focus on Service-Based Applications (SBAs). We argue that RE activities should be supported at run-time to handle context changes and to support adaptation for SBAs. We survey the state of the art for what concerns the elicitation, modeling, and analysis of requirements and will highlight some issues and challenges in order to support adaptation for SBAs.