In many contact problems when friction is not to be neglected the slip phenomenon has not been well understood. The purpose of this paper is to study the slip phenomenon by focusing on a special contact problem; namely, an unbonded circular inclusion in an infinite medium, subjected to a uniaxial tension. The interface between the inclusion and the exterior material is partitioned into regions of rigid linkage, slip, and separation. Determination of these regions leads to a coupled system of three sets of dual-series relations. Solutions have been obtained by using variational techniques. The regions of slip and the separation are simultaneously determined from the condition that the normal and shearing components of stress are finite throughout the interface. It is found that the regions of slip are quite sensitive to the coefficient of friction, but the effect of friction on the contact angle is rather small.