This work proposes a systematic approach to framework development which relies on the use of aspect-oriented (AO) techniques. The main goal of the approach is to improve the extensibility and configurability of objectoriented (OO) frameworks. It is composed of: (i) a set of guidelines to design and implement frameworks using aspect-oriented programming; and (ii) a generative model which allows the automatic instantiation of the framework and its respective OO and AO variabilities. Our guidelines propose the definition of extension join points (EJPs) in the framework code, which can be used to extend the framework basic functionality by means of extension aspects. The extension aspects are responsible for implementing optional, alternative and integration crosscutting features required by the framework users. Since such aspects can be automatically unplugged from the framework code, our approach makes it easier to customize the framework to specific needs. Three cases studies are presented to illustrate the applicability of our approach to the development of frameworks from different domains. The approach is also evaluated through both a qualitative and a quantitative study. Finally, several lessons learned and discussions resulting from the use of the approach are described.