Current debates on validity theory in language assessment have focussed on the role of social values and social policies in the use of language assessments, what McNamara and Ryan (2011) refer to as the question of the justice of the assessments. Another aspect of the validity of an assessment is its technical quality, the capacity of the assessment to produce reliable and meaningful information about candidates based on their test performance. This aspect of test validity McNamara and Ryan (2011) refer to as the fairness of the assessment. What role can Rasch measurement play in ensuring the fairness and justice of tests? This paper argues that Rasch measurement can play a central role in underpinning test fairness in particular. It extends a previous survey by McNamara and Knoch (2012) to consider recent research in language assessment using Rasch measurement techniques which illustrate how Rasch measurement can be used to investigate questions of fairness. Examples are given involving an examination of rater effects (rater variability, rater behaviour over time, rater language background), test instrument quality, test method effects and gender as a factor in performance. It is argued that competence in Rasch measurement is not simply a technical skill, but a fundamental requisite for ensuring the fairness of tests.