The Domain Name System (DNS) is a ubiquitous part of everyday computing, translating human-friendly ma- chine names to numeric IP addresses. Most DNS re- search has focused on server-side infrastructure, with the assumption that the aggressive caching and redundancy on the client side are sufficient. However, through sys- tematic monitoring, we find that client-side DNS fail- ures are widespread and frequent, degrading DNS per- formance and reliability. We introduceCoDNS, alightweight,cooperativeDNS lookup service that can be independently and incremen- tally deployed to augment existing nameservers. It uses a locality and proximity-aware design to distribute DNS requests, and achieves low-latency, low-overhead name resolution,evenin the presenceof local DNS nameserver delay/failure. Using live traffic, we show that CoDNS reduces average lookup latency by 27-82%, greatly re- duces slow lookups, and improves DNS availability by an additional '9'. We also show that a widely-deployed serviceusingCoDNSgainsincreasedcapacity,higherre- liability, and faster start times.