Though the Robotic Sailing conference held in 2011 was only the fourth in a series of robotic sailing conferences, the organizers of this important event have noticed a significant increase in the number of people working on and interested in the field of robotics sailing. This official publication contains the proceedings of the Fourth conference and was released with the intention to duly summarize the state of the art in this area. The first introductory part of the volume provides all interested parties with a good review that illustrates the history as well as very latest developments in robotic sailing. It is very important to clearly understand that possessing a reliable and robust boat shall be considered a basic and key requirement - this is what the part two of the book is mainly focusing on. The proposed boat designs are ranging from smaller one-design boat for development of the algorithms to the ships able to sail across the Atlantic Ocean. Part three of the book discusses some technical aspects of the system design and validation. The other papers that have been included in this part concentrate on algorithmic issues. The remaining parts of the book deal with the approaches applied to collision avoidance, localization and route planning.