A new type of optical waveguide, called the coupled-resonator optical waveguide (CROW), is proposed. It consists of a sequence of weakly coupled high-Q optical resonators. The waveguiding is achieved through weak coupling between otherwise localized high-Q optical cavities. The dispersion and group velocity of the photonic band of the CROW are characterized solely by the coupling factor κ₁. The CROW allows for highly efficient nonlinear optical frequency conversion and perfect transmission through bends. Two mechanisms for optical waveguiding are discussed: total internal reflection and Bragg reflection. The CROW is realized through evanescent-field coupling between high-Q whispering-gallery modes of individual microdisk cavities or through defect cavities embedded in a 2D photonic crystal. The CROW's eigenmode is similar to the high-Q mode in a single resonator, but the coupling between individual high-Q modes is considered. The waveguide mode satisfies the Bloch theorem, and the dispersion relation is derived. The group velocity is found to be small for weakly coupled CROWs. The CROW allows for lossless and reflectionless bends due to its rotational symmetry. Another application is nonlinear optical frequency conversion, where the unique dispersion characteristics of the CROW can satisfy the phase-matching condition. The CROW can also be used as a superresonator, formed by folding a CROW back upon itself. The research was supported by the U.S. Army Research Office and the U.S. Office of Naval Research.A new type of optical waveguide, called the coupled-resonator optical waveguide (CROW), is proposed. It consists of a sequence of weakly coupled high-Q optical resonators. The waveguiding is achieved through weak coupling between otherwise localized high-Q optical cavities. The dispersion and group velocity of the photonic band of the CROW are characterized solely by the coupling factor κ₁. The CROW allows for highly efficient nonlinear optical frequency conversion and perfect transmission through bends. Two mechanisms for optical waveguiding are discussed: total internal reflection and Bragg reflection. The CROW is realized through evanescent-field coupling between high-Q whispering-gallery modes of individual microdisk cavities or through defect cavities embedded in a 2D photonic crystal. The CROW's eigenmode is similar to the high-Q mode in a single resonator, but the coupling between individual high-Q modes is considered. The waveguide mode satisfies the Bloch theorem, and the dispersion relation is derived. The group velocity is found to be small for weakly coupled CROWs. The CROW allows for lossless and reflectionless bends due to its rotational symmetry. Another application is nonlinear optical frequency conversion, where the unique dispersion characteristics of the CROW can satisfy the phase-matching condition. The CROW can also be used as a superresonator, formed by folding a CROW back upon itself. The research was supported by the U.S. Army Research Office and the U.S. Office of Naval Research.