Sabu M. Thampi has posted a very short introduction to Swarm Intelligence (PDF format). In his paper, he describes the biological origins of swarm intelligence in flocks of birds, schools of fish, and swarms of bees. He goes on to describe the importance of swarm intelligence to robotics, using the computational models of ant colony optimization (ACO) and particle swarm optimization (PSO). Pseudo code for the ACO algorithm is included. CC licensed image of swarming grackles by flickr user AlphaTangoBravo