We introduce a new algorithm for an unbounded concurrent double-ended queue (deque). Like the bounded deque of Herlihy, Luchangco, and Moir on which it is based, the new algorithm is simple and obstruction free, has no pathological long-latency scenarios, avoids interference between operations at opposite ends, and requires no special hardware support beyond the usual compare-and-swap. To the best of our knowledge, no prior concurrent deque combines these properties with unbounded capacity, or provides consistently better performance across a wide range of concurrent workloads.