**1. Introduction**

In recent years, the presence of mobile robots in diverse scenarios has considerably increased, to solve a variety of tasks. Among them, many developments have been carried out over the past few years in the fields of ground, underwater, and flying robotics.

Independently on the environment where they move, navigation is one of the fundamental abilities that mobile robots must be endowed with, so that they can carry out high-level tasks autonomously, in a specific environment. This problem can be addressed efficiently through the following actions. First, it is necessary to perceive the environment in which the robot has to move, and extract some relevant information from it (mapping problem). Second, the robot must be able to solve the localization problem within this environment (localization problem). With this information, a trajectory towards the target points must be planned (path planning), and the vehicle has to be guided along this trajectory, in a reactive way, considering either possible changes or interactions with the environment or with the user (control).

To perceive the environment, some kinds of onboard sensors can be used, such as laser rangefinders, visual systems, or RGB-D platforms. This perception task can be carried out either beforehand or once the navigation task has started, while the robot moves through the environment, and the result is a model or map of the environment. Regarding the localization task, it must be designed considering several issues: the available sensors, the structure of the map, and the movement constraints that the robot presents (i.e., trajectories in 3D or 6D). Furthermore, integrated exploration systems consider all these issues jointly, and they develop trajectory planning and control, while a model of the environment is obtained, and the robot estimates its position and orientation within it.

Finally, the existence of versatile tools to simulate any new development in mobile robots navigation is crucial to quickly test and compare navigation algorithms.

In light of the previous information, this special issue was introduced to present current frameworks in these fields and, in general, approaches to any problem related to the navigation of mobile robots. There were 39 papers submitted to this special issue, from which 14 papers were accepted (i.e., 36% acceptance rate), which addressed a variety of topics, as detailed in the next sections.
