Sensors play a significant role in everyday life. Nowadays, there has been a strong demand for highly selective, sensitive, responsive, stable and cost effective sensors. As a result, research emphasis is on developing new sensing materials and technologies. Carbon nanotubes (CNTs) have many distinct properties that may be exploited to develop next generation of sensors. They exhibit extraordinary strength and unique combination of excellent mechanical, electrical, thermal, optical and electrochemical properties even in its small dimension nature, which has generated increasing interest in the application of CNTs as sensors. The main thrust of this review is to highlight the present and future research and development work in the area of CNT based sensors. Different types of sensors such as biosensors, chemical sensors, mass sensors, temperature sensors, strain sensors and pressure sensors based on CNTs are also discussed in detail. This manuscript concludes with an outline of the advantages of these CNT based sensors for real-world applications. This review aims to act as a reference source for researchers to help them in developing new applications of sensors based on CNTs.