As optical network deployment gains momentum, the efficient routing of optical connections across national and global networks assumes fundamental importance. When networks are partitioned into domains, for vendor interoperability, protocol scaling, or administrative ease, the nature and degree of topology and resource abstraction in routing protocols must be balanced by the need for intelligent information sharing to enable effective path computation. Here we focus on interdomain optical routing. We first highlight some major differences between optical circuit routing and Internet Protocol (IP) datagram routing and examine neighbor discovery and diverse routing in the optical case. We then develop a taxonomy of the information that can be shared between domains, and we discuss several applications of interdomain optical routing for the single-carrier case. Finally, we highlight some key issues for the multicarrier case.