This article discusses the five studies included in this issue. Each article addressed the same topic, population invariance of equating. They all used data from major standardized testing programs, and they all used essentially the same statistics to evaluate their results, namely, the root mean square difference and root expected mean square difference (Dorans & Holland, 2000). The major premises underlying all of these articles are that population invariance is a prerequisite for equating, and lack of population invariance can be taken as evidence that a linking is not an equating.