Abstract. Several applications in areas such as biochemistry, GIS, involve storing and querying large volumes of sequential data stored as path collections. There is a number of interesting queries that can be posed on such data. This work focuses on reachability queries: given a path collection and two nodes s, t, determine whether a path from s to t exists and identify it. To answer these queries, the path-first search paradigm, which treats paths as first-class citizens, is proposed. To improve the performance of our techniques, two indexing structures that capture the reachability information of paths are introduced. Further, methods for updating a path collection and its indices are discussed. Finally, an extensive experimental evaluation verifies the advantages of our approach.