Parallelism in object-oriented systems is discussed. The most appealing way to insert parallelism in an object framework is to associate execution capacity with objects. This approach introduces active objects. Synchronous and asynchronous communication between active objects are described using examples of existing languages. A second dimension of parallelism comes from accommodating several activities within the same object. The synchronization techniques for the internal activities are described. The presented examples are written in a highly parallel language, called Parallel Objects. A distinctive characteristic of PO is the possibility of inheritance for the specification of concurrency internal to objects.< &gt;