As software systems grow in size and use more third-party libraries and frameworks, the need for developers to understand unfamiliar large codebases is rapidly increasing. In this paper, we present a tool, Relo, that supports developers? understanding by allowing interactive exploration of code. As the developer explores relationships found in the code, Relo builds and automatically manages the context in a visualization, thereby helping build the developer?s mental representation of the code. Developers can group viewed artifacts or use the viewed items to ask Relo for further exploration suggestions, with Relo providing features to limit the growth of the diagram. To ensure developers don?t get overwhelmed, Relo has been built with a user-centered approach, and preliminary evaluations with developers exploring new code have shown them to find the tool intuitive and helpful.