Robot-sumo or robo-sumo is a sport in which two robots attempt to push each other out of a circle.

The engineering challenges are for the robot to find its opponent (usually accomplished with infrared sensors) and to push it out of the flat arena. A robot should also avoid leaving the arena, usually by means of a sensor that detects the edge.

Robot-sumo is divided into classes, fought on progressivly smaller arenas:

• Standard class robots may mass up to 3 kg and fit inside a 20 cm by 20 cm box, any height.
• Mini-sumo. Up to 500 g mass, 10 cm by 10 cm, any height.
• Micro-sumo. Must fit in a 5 cm cube.
• Nano-sumo. Must fit in a 2.5 cm cube.
• Femto- sumo. Must fit inside a 1 cm cube.

Classes are further divided into remote-controlled and autonomous robots.

Sumo robots are built from scratch, from kits or from Lego components, particularly the Lego Mindstorms sets.