This contribution explores the concept of selection as an integral part of Haugen’s standardisation model from a theoretical as well as an empirical angle. It focuses on different types of factors of selection and how they are relevant to the study of selection processes both on the level of individual variants and whole varieties. The question of why standard languages appear to differ systematically from vernaculars and at the same time exhibit remarkable resemblances among each other is addressed, and characteristic features of standard languages are traced to general conditions of standardisation processes. A case study on the standardisation of German relativisers illustrates how different factors of selection combine in the dynamics of linguistic structure, variation, attitudes, and codification. It also shows how general tendencies of selection can lead to similar structures across standard languages, while it becomes clear that register variation and the historical development and changing evaluation of stylistic varieties can be crucial in order to explain the selection or de-selection of linguistic forms.