This paper describes the design and the semantics of MetaKlaim, an higher order distributed process calculus equipped with staging mechanisms. MetaKlaim integrates MetaML (an extension of SML for multi-stage programming) and Klaim (a Kernel Language for Agents Interaction and Mobility), to permit interleaving of meta-programming activities (like assembly and linking of code fragments), dynamic checking of security policies at administrative boundaries and "traditional" computational activities on a wide area network (like remote communication and code mobility). MetaKlaim exploits a powerful type system (including polymorphic types a la system F) to deal with highly parameterized mobile components and to dynamically enforce security policies: types are metadata which are extracted from code at run-time and are used to express trustiness guarantees.