PrefaceFifteen years ago, RoboCup started with the vision "By the mid-21st century, a team of fully autonomous humanoid soccer players shall win the soccer game [..] against the winner of the most recent World Cup," a landmark project that has attracted a large number of international researchers over the years, the RoboCup community. Since the beginning, enormous progress has been made. RoboCup has also broadened its focus by addressing education (RoboCupJunior) as well as research fields closer to applications (RoboCupRescue and RoboCup@Home).The RoboCup Symposium is the scientific core meeting of the RoboCup community. While the RoboCup competitions and demonstrations showcase the effectiveness of the systems in practice, the RoboCup Symposium answers the question of how they work. Each year the RoboCup Symposium is held on a different continent. In 2011, with Istanbul playing host, the 15 th RoboCup Symposium became the first to take place on two continents at once.We decided to organize the Symposium as a single track conference in 2011. The great advantage of this is that it allowed all participants to attend all sessions of the symposium. Thus, we blured the classic separation of RoboCup into the three major areas of soccer, rescue, and service robotics. To further blur these distinctions, oral presentations in the three sessions were not divided by particular topic, but jumped between different areas and leagues. This approach demonstrated the breadth and depth of research within the RoboCup community and is reflected by the sequence of the papers in this book.The consequence of a single-track schedule is that it results in a smaller number of talks. This was offset by presenting the majority of papers during two poster sessions, which allowed for greater interactions between presenters and their audience. To underline the importance of the poster presentations and to make the participants' choice about which posters to visit more informed, each poster session was preceded by a plenary presentation of so-called poster teasers, i.e., micro-talks of one minute and one slide per poster.For the 15th RoboCup Symposium, we received 97 paper submissions, covering all areas of RoboCup research. All papers were carefully reviewed by the International Program Committee. Each submission was examined by three members of the Program Committee and the final decision was made by the Co-chairs. Twelve papers were selected for oral presentation and 32 for poster presentation. The authors Jörg Stückler and Sven Behnke received the best paper award for their contribution on "Compliant Task-Space Control with Back-Drivable Servo Actuators."The RoboCup Symposium has a long tradition of inviting keynote speakers from outside the RoboCup community who have made outstanding contributions in the field of artificial intelligence. The speakers at the RoboCup 2011 Symposium, Luc Steels and Dieter Fox, talked about their ongoing research.