Since 1999, the Web Systems Evolution (WSE) series of events has provided a vibrant forum to present original work and promote discussion on topics related to the disciplined evolution of large-scale Web-based systems. WSE attracts researchers and practitioners from different domains, widely ranging from software maintenance and evolution to Web engineering and service-oriented computing. The technical program of WSE 2013 will include invited talks, paper presentations, panel discussions, and working sessions. Architecture is the special theme for WSE 2013. Over the last decade, since this theme was covered at WSE 2003 in Amsterdam, there have been profound advances related to the architecture of Web systems, evolving them toward Web 2.0, service orientation, cloud computing, and mobile platforms. We invite novel research on architectural aspects in Web systems evolution.