The mechanical behaviour of poly(vinyl butyral) (PVB) at small (< 0.1%) and large strains (> 200%) is investigated experimentally over a range of strain rates to provide data for the development and validation of constitutive models. The small-strain response is investigated using dynamic mechanical analysis at frequencies from 1 to 100 Hz and temperatures from -80 to 70 A degrees C. It is found that a generalised Maxwell model adequately describes the material behaviour in the small-strain regime. The large-strain response is investigated using a high-speed servo hydraulic test machine at strain rates from 0.2 to 400 s(-1). It is found that the PVB response is characterised by a time-dependent steep initial rise in stress followed by a hyperelastic type response until failure. No current material model completely captures this time-dependent behaviour at large strains.