An inversion is a genome rearrangement that flips around an entire contiguous interval of DNA on a single chromosome. Inversions are the most common form of large-scale genomic mutation, and as such we may study the minimum number of possible inversions separating two chromosomes.

Assuming that an ordering of genes on a chromosome is modeled by a permutation (or more likely a signed permutation since the orientations of the genes are important), inversions are modeled by reversals on these permutations. Asking for the minimum number of possible inversions separating two chromosomes gives rise to the reversal distance.