Next generation cloud systems will require a paradigm shift in how they are constructed and managed. Conventional control and management platforms are facing considerable challenges regarding flexibility, dependability and security that next generation systems will require. The cloud computing paradigm has gone part of the way towards alleviating some of the problems associated with resource allocation, utilization and managements (e.g., via elasticity). However, many of the elements of a well-designed cloud environment remain “stiff” and hard to modify and adapt in an integrated fashion. This includes underlying networking topologies, many aspects of the user control over IaaS, PaaS or SaaS layers when such is needed, construction of XaaS services, provenance and meta-data collection, and so on. In many situations the problem may be because service abstraction is inadequate. Software Defined Systems (SDS) are systems that have added software components which help abstract actual IT equipment and other layers. One classical example, of course, are hypervisors. Such separation provides a great opportunity for system administrators to more easily construct and managing their systems through flexible software layers. Software Defined Systems include Software Defined Networking (SDN), Software Defined Storage, Software Defined Servers (Virtualization), Software Defined Datacenters (SDD), Software Defined Security (SDSec), and ultimately Software Defined Clouds (SDCloud) to name a few possibilities. Individual solutions and seamless integration of these abstractions remains in many respects a challenge. After the high success of the previous editions (SDS'2014 and SDS'2015), The third International Sympoium on Software Defined Systems 2016 (SDS'2016) will continue to be a forum for scientists, researchers, students, and practitioners to present their latest research results, ideas, and developments in the area of software defined systems – both components and their integration - and by implication advancement of next generation clouds.