In our earth, less than One-third (29%) of its surface is covered by land and the remaining more than two-third (71%) remains water bodies like ocean, river, lake, etc. The oceans are rich in almost all resources that are available in land. Hence, there is a need to discover unexplored underwater assets, treasures, minerals etc. In the past recent years, the development in underwater technology and understanding of the ocean by human has made many researchers and industries to look into exploration of the ocean. Underwater exploration also helps to realize the environmental degradation in how humans are affecting and being exaggerated by changes in the ocean environment. The underwater has many applications in the field of defense, survey, archaeology, mines, navigation, animal bio acoustics etc. To mention a few which has more impact on the society are tsunami buoys, desalination system, protection of the coastal region etc. All the application involves various types of underwater sensors. This talk is going to concentrate on the fundamental to advanced underwater sensors that are used for different applications from shallow water to deep water. This presentation also deals with real time data collection using important underwater sensors and its post processing for accurate detection of the required application. The talk will touch on the hydrophones that are used for ambient noise data collection and its effect on the signal transmission in underwater channel. The Grab and Water sample Collector for Geo acoustic Inversion Study, SVP & CTD for Underwater acoustic signal analysis, an unique Underwater Battery that uses Ocean water as electrolyte, Side Scan Sonar (SSS) to obtain high-resolution seabed images, Multibeam Echo Sounder (MBES) for Seafloor mapping, Optical Cameras and Remotely Operated Vehicles (ROV) to acquire data for image processing, and Permanent Magnetic Linear Generator (PMLG) to harvest energy from sea wave. Autonomous Underwater Vehicles (AUVs) and remotely operated vehicles (ROVs) are extensively used in the scrutiny of submarines, pipelines, seabed mapping, and underwater image analysis. The acoustic signal transmission in underwater is strongly affected by the interaction of sea-bottom sediments. The geo-properties like mean grain size, porosity, grain density of marine sediments affect the sound propagation. These properties vary from location to location; this is dependent on depositional characteristics of the particular location. The above are some of the underwater sensors that will be discussed in the talk along with its application and impact on underwater research.