The need for lightweight materials for a variety of applications has resulted in the use of structural adhesives to bond prototype structures. Adhesives developed to accommodate the stringent requiremetns of such high-technology applications are usually deficient in one or two of three very crucial properties: strength, moisture resistance, and toughness. So far, advances in adhesives formulations that have ameliorated one of these deficiencies have generally adversely affected the others. Hence, a considerable amount of effort is being expended in the search for strong, moisture-resistant, tough adhesives. As adhesvies become tougher and less brittle, evaluating their performance in terms of fracture parameters becomes more complicated. Linear elastic fracture mechanics (LEFM), which is widely used to characterize these materials, does not fully describe adhesive performance as more and more ductility or plastic deformation is introduced. In the study reported here, we introduce the energy separation method for characterizing the fracture resistance of adhesives and compare it with currently used elastic and plastic fracture parameters, such as G and the J Integral. Both neat and bonded 1/2T CT plan specimens were tested and compared in this work.