**Abstract**

So far, we have been engaged in the research and development of various kinds of robots that could be applied to in-pipe inspections that existing methods (screwdrive type, parallel multi-modular type, and articulated wheeled type) cannot perform. In this chapter, we categorized each in-pipe inspection robot depending on its configuration and structure, which includes the design of the propulsive mechanism, steering mechanism, stretching mechanism, and the locations of the wheel and joint axes. On the basis of this classification and from a developer's point of view, we also discussed the various kinds of robots that we have developed, along with their advantages and disadvantages.

**Keywords:** robotic inspection, mechanical design, robots used in limited space, mobile robots, image processing
