Alerting Services inform users of Digital Libraries about new or changed content of their favorite Digital Library collection, or about new documents discussing a topic they are interested in. The users define their interest in form of subscriptions; the alerting service filters new or changed documents against all user subscriptions and notifies the users about matches found. To define their subscriptions, users may, e.g., select a journal from a list, or a topic from a classification. Few services support the definition of IR type queries, or advanced combinations of queries and metadata selections.