Magnetic navigation (MagNav) is an emerging technology that can provide positioning information when GPS is unavailable. GPS may be unavailable due to jamming, in underwater environments, in indoor locations, or in other situations with signal may be unreliable. MagNav operates by matching magnetic sensor measurements in a moving platform to detailed magnetic maps and/or models. For this system to work effectively, high-quality maps/models, accurate sensor measurements, and optimum navigation algorithms are essential. Currently, MagNav is still in the prototype stage, although its feasibility has been demonstrated in a number of tests, both by government and private industry. The ability to navigate in GPS-poor environments is essential for military and private navigation.