This thesis proposes a new paradigm, Modelware, for reducing the complexity of middleware design and implementation. The Modelareware approach distinguishes between the core architecture design and the crosscutting architectural elements. The crosscutting elements are scattered around the entire middleware code base, can not be easily encapsulated through the traditional software decompostion model. Aspect-Oriented Programming (AOP) allows the different abstraction models to be superimposed on top of one another. By utilizing this capability of AOP, the Modelware approach successfully encapsulates the crosscutting features to coherent modules that matches the design specifications of these features. Both the core and aspect-oriented design in Modelware utilize the Model Driven Architecture methodologies to further reduce the complexity of middleware implementation. The Modelware Customization Framework, proposed in this thesis, ensures that the aspect-oriented features can be correctly composed together. To evaluate Modelware methodologies, two middleware systems, CORBA and JMS, are implemented in Modelware, as case studies.