In this paper, we argue that an exclusively inactive interface to directory services can hinder server scalability and indirectly restrict the behavior of potential applications. We propose to extend directory services' interfaces with a proactive mode by which clients can express their interest in (and be notified of) changes in the environment. These notification channels can be subsequently customized on a per-client basis through client-specified filters. Finally, in order to simplify the handling of client/server failures we adopt a leasing model for client registration to (and customization of) a notification channel. To validate our approach, we have designed and implemented the Proactive Directory Service (PDS).