A basic requirement for an autonomous mobile robot is to localize itself with repect to a given coordinate system. In this regard two different operating conditions exist: structured and unstructured environment. The relative method and algorithms are strongly influenced by the a priori knowledge on the environment where the robot operates. If the environment is known, a proper multisensor system endowed with an efficient data fusion algorithm may provide a very accurate localization. In this chapter the localization problem is formulated in a stochastic setting and a Kalman filtering approach is proposed for the integration of odometric, gyrocope, sonar and video camera measures. If the environment is only partially known the localization ...