The computer program avida is an auto-adaptive genetic system designed primarily for use as a platform in Digital or Artificial Life research. The avida system is based on concepts similar to those employed by the tierra program developed by Tom Ray. It is a population of self-reproducing strings with a Turing-complete genetic basis subjected to Poisson-random mutations. The population adapts to the combination of an intrinsic fitness landscape (self-reproduction) and an externally imposed (extrinsic) fitness function provided by the researcher. By studying this system, one can examine evolutionary adaptation, general traits of living systems (such as self-organization), and other issues pertaining to theoretical or evolutionary biology and dynamic systems.