Optical frequency combs have emerged as an important tool enabling diverse applications from test-and-measure-ment,including spectroscopy,metrology,precision distance measurement,sensing,as well as optical and microwave wave-form synthesis,signal processing,and communications.Several techniques exist to generate optical frequency combs,such as mode-locked lasers,Kerr micro-resonators,and electro-optic modulation.Important characteristics of optical frequency combs in-clude the number of comb lines,their spacing,spectral shape and/or flatness,and intensity noise.While mode-locked lasers and Kerr micro-resonators can be used to obtain a large number of comb lines compared to electro-optic modulation,the lat-ter provides increased flexibility in tuning the comb spacing.For some applications in optical communications and microwave photonics,a high degree of integration may be more desirable over a very large number of comb lines.In this paper,we re-view recent progress on integrated electro-optic frequency comb generators,including those based on indium phosphide,lithi-um niobate,and silicon photonics.