The overall outage probability (OOP) and symbol error probability (SEP) of a two-way amplify-and-forward (AF) relaying system are investigated. Tight closed-form expressions for the OOP and average SEP are derived for single-relay two-way AF systems. Further, in the case of multiple-relay two-way relaying, a tight closed-form expression for the OOP and an asymptotic approximation to the average SEP are obtained, respectively. Using these expressions, one can evaluate the outage and SEP performance of a two-way relaying system easily and fast.