Corrosion has been a great concern in the oil and natural gas industry. A variety of corrosion sensor technologies have been developed based on different sensing principles. Conventional corrosion sensors and emerging sensor technologies are critically reviewed in terms of sensing principles, sensor designs, advantages, and limitations. Conventional corrosion sensors encompass corrosion coupons, electrical resistance probes, electrochemical sensors, ultrasonic testing sensors, magnetic flux leakage sensors, electromagnetic sensors, and inline inspection tools. Emerging sensor technologies include optical fiber sensors (OFS) and passive wireless sensor technology such as surface acoustic wave (SAW) sensors. OFS have advantages of nondestructive monitoring, in-situ distributive measurements, long reach, small size, light weight, inherent immunity to electromagnetic interference, compatibility to optical fiber data communication systems, and improved safety in the presence of flammable gas/oil as compared to electrical based sensors. Passive SAW sensors have advantages of small size, cost efficiency, ease of fabrication, compatibility with wireless telemetry, and adaptability to many applications. Both emerging technologies are promising in corrosion monitoring in the oil and natural gas applications. The ability to monitor corrosion online before the structural integrity is compromised can have a significant impact on preventing catastrophic events resulting from corrosion. Distributed chemical sensing shows promising potential to detect early corrosion onset and monitor corrosive environments for corrosion mitigation management. Additionally, high durability and stability are required for corrosion sensors in extreme service conditions such as high temperature and high pressure during drilling, production, and refining.