The INGRES DBMS provides the capability for customers to extend the system through the addition of their own functions and/or datatypes. The system also allows users to configure the database to notify applications when "interest- ing" events occur. The notified applications can then take some action based on the event. These capabilities represent the entry of the INGRES system into the realm of extensible data managers. We believe that extensibility will be a necessity in the coming generation of general purpose systems. This talk will discuss the capabilities and mechanism presented in the current INGRES product, some current uses in the "real world", and the future of extensibility in the commercial database arena.