NESL has been researching the field of inertial navigation system for the last 20 years. Inertial navigation system has the benefit of being able to obtain the position, velocity, and attitude of a vehicle with the outputs of gyroscopes and accelerometers alone. In case of pure inertial navigation, the navigation solution diverges due to various error factors. To compensate for these shortcomings, high-precision aided inertial navigation using GNSS, database, visual sensors, star sensors, sun sensors, and, in the case of pedestrian navigation, the characteristics of a user’s movement, etc. has been researched. In addition, we are working on data fusion technologies incorporating such various sensors, and also on making systems more reliable through anti-jamming and anti–spoofing, and fault detection.