Devices have been formed in Ti-diffused and proton-exchanged lithium niobate for applications in optical communications, sensing and signal processing. Most active devices make use of the electrooptic effect. The design and operation of various modulators, couplers and Y-branch power dividers will be described. Sometimes, device characteristics are tailored to meet specific requirements, e.g. phase-bias trimming of a linear modulator sensor. Proton-exchanged waveguides are generally used where high optical powers are transmitted.