This volume contains the papers presented at SAT 2009: 12th International Conference on Theory and Applications of Satis?ability Testing, held from June 30 to July 3, 2009 in Swansea (UK). The International Conference on Theory and Applications of Satis?ability Testing (SAT) started in 1996 as a series of workshops, and, in parallel with the growthof SAT, developedinto the main eventfor SAT research. This year'sc- ference testi?ed to the strong interest in SAT, regarding theoretical research, - searchonalgorithms, investigationsintoapplications, anddevelopmentofsolvers and software systems....