Welcome to participate in DependSys 2015, Zhangjiajie, China, November 18-20, 2015! Zhangjiajie is an emerging tourist destination famous for its unique natural scenery and abundant tourism resources. It is located in the northwest of Hunan province, about 400 kilometers away from Changsha, the capital of Hunan province, covering a total area of 9,563 square kilometers, of which 76% are mountainous area. Zhangjiajie was listed into the World Natural Heritage Catalogue by the UNESCO in 1992. Zhangjiajie was awarded the title of "World Geological Park" in 2004. DependSys 2015 offers a timely venue for bringing together new ideas, techniques, and solutions for dependability and its issues in sensor, cloud, and big data systems and applications. As we are deep into the Information Age, we witness the explosive growth of data available on the Internet. Human beings are producing quintillion bytes of data every day, which come from sensors, individual archives, social networks, Internet of Things, enterprise and Internet in all scales and formats. One of the most challenging issues we face in achieving designed system performance to an expected level, i.e., how to effectively provide dependability in sensor, cloud， big data systems and applications. These systems need to typically run continuously, which often tend to become inert, brittle, and vulnerable after a while. We can observe that this trend is further stimulated by an ever-increasing cost pressure. This symposium provides a forum for individuals, academics, practitioners, and organizations who are developing or procuring sophisticated computer systems on whose dependability of services they need to place great confidence. Future systems need to close the dependability gap in face of challenges in different circumstances. The emphasis will be on differing properties of such services, e.g., continuity, effective performance, real-time responsiveness, ability to overcome data fault/corruption/anomaly, ability to avoid catastrophic failures, prevention of deliberate privacy intrusions, reliability/availability/sustainability/adaptability/heterogeneity/security/safety, and so on.