  A simple model of an atomic Bose-Einstein condensate in a box whose size
varies with time is studied to determine the nature of adiabaticity in the
nonlinear dynamics obtained within the Gross-Pitaevskii equation (the nonlinear
Schr\"{o}dinger equation). Analytical and numerical methods are used to
determine the nature of adiabaticity in this nonlinear quantum system. Criteria
for validity of an adiabatic approximation are formulated.
