Today, thanks to the development of micro-scale low-cost accelerometers, gyroscopes, and magnetometers, it is possible to construct compact motion-sensor arrays with hundreds of sensing elements. These arrays, as well as providing a high performance-to-price ratio, can also provide new measurement capabilities and enable the development of smart sensors that adapt to the usage conditions. This paper gives an overview of the capabilities enabled by the stochastic, component, temporal, and spatial information diversity that an array of inertial or magnetic field sensors provide. The main challenges in the practical realization of these types of arrays are described.