Researchers and professionals will find in this text the thoroughly refereed post-proceedings of the Third International Conference on the Quality of Software Architectures, QoSA 2007, held in Medford, MA, USA, in 2007. It was mounted in conjunction with the 10th International ACM SIGSOFT Symposium on Component-Based Software Engineering, CBSE 2007. The 13 revised full papers presented together with one keynote lecture were carefully reviewed and selected from 42 submissions.