A debugger and method for debugging computer programs across multiple programming languages are provided. The debugging is performed at a source level of a computer program written in any programming language supported by the .Net.RTM. platform, while the program is executed over a Java runtime environment. The debugger disclosed provides a call stack display and an expression evaluator. Furthermore, the debugger allows software developers to step through Java source code and follow the execution flow of the Java program. One exemplary embodiment of the disclosed debugger is an extension of the Microsoft.RTM. Visual Studio .Net.RTM..