Multi-version graph processing, where each version corresponds to a snapshot of an evolving graph, is a common scenario in large-scale graph processing. Straightforward application of existing graph processing systems often yields suboptimal performance due to high version-switching cost. We present Version Traveler (VT), a graph processing system featuring fast and memory- efficient version switching. VT achieves fast version switching by (i) representing differences among versions as deltas and (ii) constructing the next version by integrating the in-memory graph representation of the current version with the delta(s) relating the two versions. Furthermore, VT maintains high computation performance and memory compactness. Our evaluation using multi-version processing workloads with realistic datasets shows that VT outperforms PowerGraph- running 23x faster with a 15% memory overhead. VT is also superior to four multi-version processing systems, achieving up to 90% improvement when jointly considering processing time and resource consumption.