Distributed heterogeneous search environments are an emerging phenomenon in Web search. They can be viewed as a federation of independently controlled metasearchers and many specialised search engines. Specialised search engines provide focused search services in a specific domain (e.g. a particular topic). Metasearchers help to process user queries effectively and ef.ciently by distributing them only to the most suitable search engines for each query. Compared to the traditional search engines like Google or AltaVista, specialised search engines (together) provide access to arguably much larger volumes of high-quality information resources, frequently called the "deep" or "invisible" Web [10]. We envisage that such heterogeneous environments will become more popular and influential.