The thesis describes an investigation of on-line help provision for computer systems that have graphical object-oriented interfaces. It concentrates on object-based help facilities and describes the development of a method for obtaining object-based help information and the identification of useful types of object-based help information. The thesis demonstrates that it is both possible and practical to obtain object-based help information from the code of an appropriately programmed main system, and it describes observational studies that showed the usefulness of some types of object-based help information. The approach that was taken involved implementing two systems in object-oriented programming styles. Both systems have graphical object-oriented interfaces' and object-based help facilities. The object-based help facilities provide information about the objects displayed by the interfaces when the display objects are indicated. The object-based help information is drawn from system objects which are coded components of the systems. This method is practical when there are one-to-one correspondences between display objects and the system objects that generate and maintain them. The term 'self-explanatory objects' denotes system objects that have been written to be used as a source of object-based help information in this way. The first system is a simple proof-of-concept prototype in the form of a noughts and crosses game. The second system, a game of strategy called Partickles, includes both object-based and menu-based help. The usage of Partickles' help facilities was investigated in a series of three successive studies conducted with a total of nineteen school students aged 12 to 18. Evidence from the studies has shown the usefulness of menu-based overviews and reference facilities, and of object-based help information that explains what display objects would do if activated in the current context. The results include suggestions for implementing help facilities based on self-explanatory objects, a set of guidelines for the provision of help in systems that have graphical object-oriented interfaces, a framework for the provision of object-based help and four types of information that can be used as a template for object-based help messages.