UML is defined as a visual modeling language for specifying, constructing, and documenting software intensive systems. In that context, UML diagrams play a central role in the whole software engineering process, starting from early analysis, through implementation, to maintenance. Recent surveys of UML use in industry showed that software practitioners use it on a regular basis, and particularly for communication and as a mental-assist tool. However, they also pointed out the following weaknesses: the lack of context, graphical layout problems, and the language’s inadequacy as a facility for communication between technical teams and their clients. In this paper, we present a general approach that addresses these problems by enhancing the effectiveness of UML models as a communication vehicle. Our approach is based on expressing stakeholder-specific viewpoints through the use of secondary notations. This involves the use of auxiliary visual variables (e.g., color, position, size) that are not formally specified in UML. To that end, we extend the traditional concept of layer found in many graphical editors to UML diagram editors. FlipLayers is an implementation of our approach. It is in the form of a plugin for the Papyrus modeling environment. One scenario with several case studies is presented in the paper to demonstrate the benefits of our approach and also to illustrate how to express viewpoints with FlipLayers.