Welding defects result infailure of the machinery and other negative consequences. Therefore, they need to be detected as they appear to ensure efficient and high-quality production. There is a raising interest in the implementation of sensors to provide highly accurate and robust real-time welding process monitoring. This work describes the four most widely used techniques of welding process monitoring. These monitoring techniques are arc sensors, optical sensors, infrared sensors, and ultrasonic sensors. This work explains their principles of operation: discuss their advantages and limitations and give typical areas of application. Arc sensors, optical sensors, infrared sensors, and ultrasonic sensors are described in detail with the necessary figures and schemes in the first part of the present study. The physical background, the strengths and weaknesses, and real life examples of the sensing techniques are given in this part. The results of the research show that each sensing method has its specific features thatcan play an important role in certain welding applications. Arc sensors do not requireadditional equipment in the welding zone. Thisis why they can be used where operational space is limited. Optical sensors allow the observation of the weld pool behavior. Infrared sensors can create the temperature profile of the weld. Ultrasonic sensors usually have good resolution and can provide accurate data. This paper will help welding engineers to choose the optimal sensing equipment for aspecific industrial application.