The successful development of a helicopter and its introduction into service may be influenced by several factors but a well co-ordinated development programme is by far the most important. A practical and realistic balance between representative ground tests and the subsequent flight proving is essential if the project is to be completed within a reasonable budget and time scale. The two parts of this paper cover these phases and aim to show how they are related in a particular development programme. The use of major fully representative ground rigs is discussed in relation to pre-flight functioning and fatigue life assessment; this is followed by the initial flight trials and finally the structural and performance clearance of the helicopter over its full design envelope. Although the tests and techniques described are generally applicable, the examples quoted relate to the Bristol Type 192, tandem rotor helicopter. The opinions expressed are personal and do not necessarily represent those of the Bristol Aircraft Limited.