Microsoft Visual J# .NET is a development tool for Java-language developers who want to build applications and services on the .NET Framework.

Microsoft Visual J# .NET is not a tool for developing applications intended to run on a Java Virtual Machine. Applications and services built with Visual J# .NET will run only in the .NET Framework and will not run on any Java Virtual Machine. Visual J# .NET has been independently developed by Microsoft.

Visual J# (sometimes known as just J#) is a set of programmming tools that allow developers to use the Java programming language to write applications that will run on Microsoft's .NET runtime platform. While Microsoft does not support the Java Virtual Machine as part of .NET, Visual J# allows a programmer familiar with or who prefers Java's concepts and language syntax to write and compile a program that will run successfully on the .NET Framework Common Language Runtime platform. The source statements are compiled into Microsoft Intermediate Language (MSIL), which is the equivalent of Java bytecode. A program already compiled into Java bytecode can be converted into MSIL.