The enthalpy landscape is used to derive from first principles the departure functions that quantify structural recovery and aging in glassy materials. The departure functions are identical in form to the phenomenological Kovacs-Aklonis-Hutchinson-Ramos model departure functions, but with the important difference is that the relaxation times do not depend on the instantaneous structure (e.g., volume). This first-principles derivation elucidates a number of experimental observations in glassy materials, including the asymmetry of approach, the effective relaxation-rate paradox, and the different time dependences for volume and enthalpy recovery. Example results that qualitatively display these phenomena are obtained with a simple enthalpy landscape. (C) 2003 Wiley Periodicals, Inc.