Issues surrounding lineup fairness have been explored scientifically for over two decades. The present study investigates the applied/external validity of this line of research. First, several factors leading to bias in the construction of photo lineups are examined, and results of a preliminary survey on current law enforcement practices are presented. Several statistics that have been developed to assess the fairness of lineups are reviewed and the application of these techniques to lineups used in 18 criminal cases is discussed, including the mixed agreement that sometimes occurs between estimates. Finally, we address the usefulness of lineup fairness assessment for expert testimony in the courtroom, and the dilemma that may be faced by the expert witness who is asked to testify by the defense. It is suggested that a useful and empirically-justified index of overall lineup fairness can be created by combining a single estimate of bias (Functional Size) and a single estimate of lineup size (Effective Size) into a four-point index.