The cycle design point defines the geometry of an engine and its components including the inlet and hence the size of the nacelle. However, it is only a single operating condition and the engine must also behave satisfactorily throughout the full operating envelope. We show how to select the cycle design point and which other factors should be considered to ensure adequate margins in flow, temperature and spool speeds. Examples are given for applications on a subsonic transport as well as a fighter aircraft. We look at the issues involved in a hybrid system with high power extraction and how the use of non-dimensional parameters helps integrate the components whose performance is dependent on the flight condition with the other elements whose operation is independent of the flight condition. Finally, we discuss how the cycle may be optimized, using the multi-point design method to combine the cycle design point with calculations at several off-design conditions.