This paper outlines the next-generation science information network, called SINET3, which will be launched in April 2007 as the integrated successor network to SINET and Super-SINET. Using leading-edge networking technologies, SINET3 will provide a rich variety of network services and will adapt flexibly to the needs of the research and education community. The network services include multi-layer services such as IP, Ethernet, and lambda services, well-prepared virtual private network services for collaborative research among related organizations, and layer-1 bandwidth on demand services for emerging high-performance applications. Introducing layer-1 switches as core network components, the network will be structurally changed into an advanced hybrid optical and IP/MPLS network and will form a nationwide innovative network infrastructure for the research and education community. This paper gives an overview of SINET3 from the viewpoints of network services, network architecture, and networking technologies.