Theseproceedingscontainthepapersofthe3rdEuropeanWorkshoponSecurity and Privacy in Ad Hoc and Sensor Networks (ESAS 2006), which was held in Hamburg, Germany, September 20–21, 2006, in conjunction with the 11th European Symposium on Research in Computer Security (ESORICS 2006). This year, a total of 44 full papers were submitted to ESAS. Each subm- ted paper was reviewed by at least three expert referees. After a short period of discussion and deliberation, the Program Committee selected 14 papers for presentation and subsequent publication in the workshop proceedings. This c- responds to an acceptance rate of 32% – a respectable rate by any measure. In addition to the presented papers, this year’s workshop also featured two keynote speeches and seven project presentations. In the ?rst keynote, Jean-Pierre Hubaux (EPFL) gave an overview of “Security and Cooperation in WirelessNetworks”.ThesecondkeynotewasgivenbyPimTuyls(Philips)onthe interesting topic of “Grey-Box Cryptography: Physical Unclonable Functions”. The project presentations covered the following European Projects: S3MS, SeVeCom, BIONETS, CASCADAS, MOBIUS, EYES and UbiSecSens. Unf- tunately, the extended abstracts of these presentations could not be included in the proceedings. As the Chairs of ESAS 2006, we are very happy with the outcome of the workshop that clearly demonstrates the continued importance, popularity, and timeliness of the topic: Security and Privacy in Ad Hoc and Sensor Networks.