One major aim of international large-scale assessments (ILSAs) is to monitor changes in student performance over time. To accomplish this task, a set of common items is repeatedly administered in each assessment and linking methods are used to align the results from the different assessments on a common scale. The present article introduces a framework for discussing linking errors in ILSAs, in which different components of linking errors are distinguished (country-by-item interaction, assessment-by-item interaction and country-by-assessment-by-item interaction). Furthermore, the different components of linking errors are used to analytically derive standard errors for national trend estimates. In a simulation study, the proposed standard error formula outperforms the method that is used in PISA. In addition, the PISA 2006 and 2009 reading data are used to illustrate how the interpretation of national trend estimates can change when different procedures are applied to calculate standard errors.