An experimental system providing assistance in the task of program construction, validation and description is presented. This system (Pearl) encourages a particular top-down approach to programming such that programs so developed exhibit a multi-level, hierarchical structure. Amongst several tools provided by the system is one ·"hich enables programs to be exercised even though they may be eXercised in terms of abstract operations and data types. The whole system is designed to be used in an interactive environment. Programs are developed by the programmer with appropriate assistance and guidance from the computer. Contemporary programming tools and methods are surveyed and their relevance to the development of high quality software is discussed. In particular attention is given to programming methodologies,design representations and issues of program correctness. The practicality of the system is demonstrated i!l a mmber of examples.