This paper describes an experimental and analytic study of Mode II fracture in a ductile aluminum beam. Mode II fracture is characterized by an in-plane sliding of crack surfaces relative to one another. For ductile materials such as aluminum, failure is preceded by yielding near the crack tip. In this paper, a Mode II fracture anaylsis technique that includes yielding near the crack tip is presented. Unlike other methods, the analysis presented in this paper (1) provides a simple method for modeling stable and unstable crack growth; (2) can be implemented with a general purpose finite-element package; (3) predicts the maximum load at failure and the nature of the failure, either unstable crack growth or yield; (4) includes interface elements to prevent overlap of the crack surfaces; and (5) includes directly the R-curve values. The finite-element modeling technique provided a reasonable, qualitative approximation of experimental behavior.