This book constitutes the thoroughly refereed post-conference proceedings of the Third International ICST Conference on Networks for Grid Applications, GridNets 2009, held in Athens, Greece, in September 2009. The 10full papers, 3 invited papers and 2 invited keynotes address the whole spectrum of Grid networks and cover various topics such as authorisation infrastructure for on-demand Grid and network resource provisioning, access control requirements for Grid and cloud computing systems, business models, accounting and billing concepts in Grid-aware networks, multiple resource scheduling in e-science applications, percolation-based replica discovery in peer-to-peer grid infrastructures, GridFTP GUI, alarms service for monitoring multi-domain Grid networks,Grid computingto explore the computational resources of the settop boxes, open source cloud computing systems based on large scale high performance, dynamic network services, WDM ring networks, architecture to integrate broadband access networks and wireless Grids, implementation of random linear network coding using NVIDIA's CUDA toolkit, collaboration in a wireless Grid innovation testbed by virtual consortium as well as challenges for social control in wireless mobile Grids