This thesis explores the design space of hybrid electrical and optical network architectures for modern data centers. It tries to reach a delicate balance between performance, fault-tolerance, scalability and cost through coordinated use of both electrical and optical components in the network. We have developed several approaches to achieving these goals from different angles. First, we used optical splitters as key building blocks to improve multicast transmission performance. We built an unconventional optical multicast architecture, called HyperOptics, that provides orders of magnitude of throughput improvement for multicast transmissions. Second, we developed a failure tolerant network, called ShareBackup, by embedding optical switches into the Clos networks. Sharebackup, for the first time, achieves network-wide full-capacity failure recovery in milliseconds. Third, we proposed to enable programmable network topology at runtime by inserting optical switches at the network edge. Our system, called RDC, breaks the bandwidth boundaries between servers and dynamically optimizes its topology according to traffic patterns. Through these three works, we demonstrate the high potential of hybrid datacenter network architectures for high performance and fault-tolerance.