—We propose a Smart Trend-Traversal (STT) protocol for RFID tag arbitration, which effectively reduces the collision overhead occurred in the arbitration process. STT, a Query Tree-based scheme, dynamically issues queries according to the online learned tag density and distribution; and therefore, it significantly reduces delay and energy consumption comparing with the existing Tree-based and Aloha-based protocols. Our analytic studies further show that the optimality of STT does not rely on any presumed network conditions, which is in sharp contrast to other available schemes and renders it a highly desirable and practical solution.