The increasing complexity of building distributed applications has positioned middleware as a critical part of complex systems. However, current middleware standards do not address properly the highly dynamic and diverse set of requirements posed by important classes of applications, such as those involving multimedia and mobility. It is clear that middleware platforms need to be more flexible and adaptable and we believe that an open engineering approach is an essential requirement. More specifically, we propose the use of object oriented reflection based on a multi-model reflection framework as a principled way to achieve such openness. This leads to middleware that is flexible, adaptable and extensible, and, in consequence, capable of supporting applications with dynamic requirements.