Navigation, according to the standardized definition given in the IEEE standard 172-1983, is the process of directing a vehicle so as to reach an intended destination. The capability of navigating an environment is a critical ability for a mobile robot, especially if the robot is performing an intended task autonomously. Endowing a robot with the capability of autonomously navigating an environment requires the solution of at least three basic tasks in mobile robotics, namely localization, mapping, and motion control. A robot is said to represent an aspect of the environment when there is a functioning isomorphism between some aspect of the environment and a robot process that adapts the robot behavior to it. This chapter focuses on environment representations useful for robotic autonomous navigation. In this scenario, environment representations can be broadly partitioned into two groups: topological representations and metrical representations.