Dynamic Querying (DQ) is a technique adopted in unstructured Peer-to-Peer (P2P) networks to minimize the number of nodes that is necessary to visit to obtain the desired number of results. In this chapter we describe the use of the DQ technique over a Distributed Hash Table (DHT) to implement a scalable Grid information service. The DQ-DHT (Dynamic Querying over a Distributed Hash Table) algorithm has been designed to perform DQ-like searches over DHT-based networks. The aim of DQ-DHT is two-fold: allowing arbitrary queries to be performed in structured P2P networks, and providing dynamic adaptation of search according to the popularity of resources to be located. Through the use of the DQ-DHT technique it is possible to implement a scalable Grid information service supporting both structured search and execution of arbitrary queries for searching Grid resources on the basis of complex criteria or semantic features.