Development is the process by which a design conceived to meet a practical requirement is transformed from drawings, and perhaps a working prototype, to a piece of fully engineered hardware suitable for production which will meet the original requirement for performance (including reliability) and cost in a time-scale which makes it useful.

There are thus three main parameters in development: performance, cost and time, which are inextricably related to each other, and which must be constantly in mind during a development programme.

The technical aspect of development consists largely of optimising a basic design, making and proving individual parts of it, particularly where new technology is involved, and finally making and proving the complete equipment.