We consider wave propagation in longitudinally periodic media near the first- and higher-order Bragg resonances. An extended coupled-waves (ECW) approach is applied to media with single or multiharmonic periodicities and numerically compared to the Floquet theory. The ECW approach predicts coupling coefficients χ that vary as ηN, where η is the magnitude of the perturbation and N is the Bragg order. Explicit expressions are also given for the band-gap width and band-gap shift for all Bragg orders. A number of applications are discussed.