Exploratory search is an information seeking behavior where users progressively learn about one or more topics of interest; it departs quite radically from traditional keyword-based query paradigms, as it combines querying and browsing of resources, and covers activities such as investigating, evaluating, comparing, and synthesizing retrieved information. In most cases, such activities are enabled by a conceptual description of information in terms of entities and their semantic relationships. Customized Web applications, where few applicative entities and their relationships are embedded within the application logics, typically provide some support to exploratory search, which is, however, specific for a given domain. In this paper, we describe a general-purpose exploratory search framework, i.e., a framework which is neutral to the application logic. Our contribution consists of the formalization of the exploratory search paradigm over Web data sources, accessed by means of services; extracted information is described by means of an entity-relationship schema, which masks the service implementations. Exploratory interaction is supported by a general-purpose user interface including a set of widgets for data exploration, from big tables to atomic tables, visual diagrams, and geographic maps; the user interaction is translated to queries defined in SeCoQL , a SQL-like language and protocol specifically designed for supporting exploratory search over data sources. We illustrate the software architecture of our prototype, which uses the interplay of a query and result management system with an orchestrator, capable of incrementally building queries and of walking through the past navigation history. The distinctive feature of the framework is the ability to extract top solutions, which combine top-ranked entity instances. We evaluate exploratory search from the end-user perspective in the context of a cognitive model for search, by studying the user’s behavior and the effectiveness of exploratory search in terms of quality of results produced by the search process; we also compare the effectiveness of interaction in using our multi-domain search system with the use of various replicas of the system, each acting upon a single domain, and with the use of conventional search engines.