A polarization modulator (PolM) incorporating with a polarizer and an optical filter can realize various functions such as phase modulation, intensity modulation with tunable chirp or frequency multiplication, tunable microwave photonic phase shifting, etc. Using a PolM to replace the intensity modulator in a traditional optoelectronic oscillator (OEO), various new features have been discovered. In this paper, the recent developments in employing PolMs for constructing different types of OEOs are reviewed and the emerging applications enabled by the PolM-based OEOs are discussed.