This book constitutes the refereed proceedings of the 12th International Workshop on Cryptographic Hardware and Embedded Systems, CHES 2010, held in Santa Barbara, USA during August 17-20, 2010. This year it was co-located with the 30th International Cryptology Conference (CRYPTO). The book contains 2 invited talks and 30 revised full papers which were carefully reviewed and selected from from 108 submissions. The papers are organized in topical sections on low cost cryptography, efficient implementation, side-channel attacks and countermeasures, tamper resistance, hardware trojans, PUFs and RNGs.