Robotics from the bottom up ...

The word "beam" in BEAM robotics is an acronym for Biology, Electronics, Aesthetics, and Mechanics. This is a term that refers to a style of robotics that primarily uses simple analogue circuits, such as comparators, instead of a microprocessor in order to produce an unusually simple design (in comparison to traditional mobile robots) that trades flexibility for robustness and efficiency in performing the task for which it was designed.

Unlike many traditional processor-based robots, BEAM robots are cheap, simple, and can be built by a hobbyist with basic skills in a matter of hours. Because of this, BEAM is an excellent way of getting started in robotics, and of learning about electronics. BEAM is the brainchild of Mark W. Tilden who is currently working as a researcher at Los Alamos National Laboratory.
While BEAM robots are often simple (consisting of a solar cell, motor, 2 transistors, and capacitor), robots as complicated as 8-jointed, 4-legged walking spiders have been built using the principles of BEAM.
To get started on building your own BEAM robot i recommend checking out this site, which explains the BEAM philosphy and has a couple of tutorials and circuit diagrams to get you started.
The BEAM robot in the image above was designed to follow a light source ... using simple electronics .. no microcontroller required :) check out the clip below :)