Since the first use of fingerprints for identification over 100 years ago, the statement that "Every fingerprint is unique" has become almost an article of faith. However this assertion has come under scrutiny following several instances of mistakes in identification by law enforcement agencies. Given two fingerprints that appear to match, the question is how likely is it that this is a chance resemblance between different fingers? It is necessary to define what is a "match", and this in turn leads down the path of deciding how to represent what the fingerprint examiners refer to as the...