In this chapter a brief review of studies analyzing the relation between disorders in mental representation of space and environmental navigation is reported. Most of the studies concern the role on navigation of unilateral neglect, that is the inability to represent and to attend to the contralesional side of the space, that often follows lesion in posterior regions of the right hemisphere. Different studies demonstrate that unilateral neglect does not affect the ability to use some basic navigational processes such as path integration, but it affects the ability to develop and use cognitive maps of the environment for navigation. A case is also described of a patient who never developed navigational skills due to a congenital brain malformation. The only remarkable deficits the patients presented concerned mental imagery, supporting the hypothesis that mental imagery plays a crusial role in navigation.