JOINT: an object oriented message passing interface for parallel programming in Java. Message-passing programming interfaces are widely used when programming parallel applications. Systems such as PVM and MPI have been successful at providing the basic capabilities needed to implement parallel applications efficiently. With the advent of Java, efforts have been conducted to define a message-passing interface to be used by applications written in that language. However, current proposals have been designed to stay as close to PVM and MPI as possible, and thus fail to exploit the capabilities offered by the Java platform. This paper introduces JOINT, a message-passing programming interface for parallel applications written in Java. JOINT is designed to be simple, intuitive and to smoothly integrate with the Java environment. The paper also presents a real parallel example implemented using JOINT to illustrate the facilities given by the interface. JOINT is already implemented as part of two different distributed parallel systems: JoiN and mJoiN.