Welcome to the European Conference on Software Architecture (ECSA), which is the premier European software engineering conference. ECSA provides researchers and practitioners with a platform to present and discuss the most recent, innovative, and significant findings and experiences in the field of software architecture research and practice. The fourth edition of ECSA was built upon a history of a successful series of European workshops on software architecture held from 2004 through 2006 and a series of European software architecture conferences from 2007 through 2009. The last ECSA was merged with the 8th Working IEEE/IFIP Conference on Software Architecture (WICSA). Apart from the traditional technical program consisting of keynote talks, a main - search track, and a poster session, the scope of the ECSA 2010 was broadened to incorporate other tracks such as an industry track, doctoral symposium track, and a tool demonstration track. In addition, we also offered several workshops and tutorials on diverse topics related to software architecture. We received more than 100 submissions in the three main categories: full research and experience papers, emerging research papers, and research challenges papers. The conference attracted papers (co-)authored by researchers, practitioners, and academics from 30 countries (Algeria, Australia, Austria, Belgium, Brazil, Canada, Chile, China, Colombia, Czech Republic, Denmark, Finland, France, Germany, Hong Kong, I- land, India, Ireland, Israel, Italy, The Netherlands, Poland, Portugal, Romania, Spain, Sweden, Switzerland, Tunisia, United Kingdom, United States).