Electro-optically tunable spectral filters have been developed over the years and now include a rather diverse collection of devices. These devices, which are of increased importance for remote sensing applications, employ linear electro-optic (Pockets) materials such that tuning is accomplished via externally controlled voltages. A brief review of the properties of linear electro-optic materials is presented followed by descriptions of tunable birefringence interference filters, Fabry-Perot devices, and other novel filter structures. Recent developments in electro-optic tunable filters are included. Issues relating to the further development of infrared tunable spectral filters are discussed.