Proof-Carrying Code (PCC) is a general approach to mobile code safety in which the code supplier augments the program with a certifícate (or proof). The intended benefit is that the program consumer can locally validate the certifícate w.r.t. the "untrusted" program by means of a certifícate checker—a process which should be much simpler, eíñcient, and automatic than generating the original proof. Abstraction Carrying Code (ACC) is an enabling technology for PCC in which an abstract model of the program plays the role of certifícate. The generation of the certifícate, Le., the abstraction, is automatically carried out by an abstract interpretation-based analysis engine, which is parametric w.r.t. different abstract domains. While the analyzer on the producer side typically has to compute a semantic fixpoint in a complex, iterative process, on the receiver it is only necessary to check that the certifícate is indeed a fixpoint of the abstract semantics equations representing the program. This is done in a single pass in a much more efficient process. ACC addresses the fundamental issues in PCC and opens the door to the applicability of the large body of frameworks and domains based on abstract interpretation as enabling technology for PCC. We present an overview of ACC and we describe in a tutorial fashion an application to the problem of resource-aware security in mobile code. Essentially the information computed by a cost analyzer is used to genérate cost certificates which attest a safe and efficient use of a mobile code. A receiving side can then reject code which brings cost certificates (which it cannot validate or) which have too large cost requirements in terms of computing resources (in time and/or space) and accept mobile code which meets the established requirements.