Scope and Applicability In order to highlight the main qualitative features of aeroelasticity in this Item the following simplifications in terms of aeroplane configuration and flight condition are introduced. (i) The aeroplane is assumed to be a classically configured transport type aeroplane which restricts the wings to medium and high aspect ratios@ typically@ > 4and up to moderate sweep-back angles@ typically. A < 35??ii) The aeroplane flight condition is restricted to subsonic@ symmetric flight at either a steady level flight condition or a quasi-steady manoeuvring condition. All Mach number effects are ignored. (iii) All flight angles@ including the angle of incidence@ the pitch angle and the flight path angle@ are assumed small. (iv) Wing and tailplane flexibilities are assumed to take the form of bending and twist about an elastic@ or flexural axis; chordwise deformations are ignored. (v) Weight distributions of all parts of the aeroplane are assumed to be unaffected by deformation effects.