The need to discover and select entities that match specified requirements arises in many contect in distributed systems. Meeting this need is complicated by the fact that not only may the potential consumer specify constraints on resources, but the owner of the entity in question may specify constraints on the consumer. This observation has motivated Raman et al. to propose that discovery and selection be implemented as symmetric matching process, an approach they take in their ClassAds system. We present here a new approach to symmetric matching that achieves significant advances in expressivities relative to the current ClassAds — for example, allowing for multi-way matches, expression and location of resource with negotiable capability. The key to our approach is that we reinterpret matching as a constraint problem and exploit constraint-solving technologies to implement matching operations. We have prototyped a matchmaking mechanism, named Redline, and used it to model and solve several challenging matching problems.