This volume advances our understanding of how word structure in terms of affix ordering is organized in the languages of the world. A central issue in linguistic theory, affix ordering receives much attention amongst the research community, though most studies deal with only one language. By contrast, the majority of the chapters in this volume consider more than one language and provide data from typologically diverse languages, some of which are examined for the first time. Many chapters focus on cases of affix ordering that challenge linguistic theory with such phenomena as affix repetition and variable ordering, both of which are shown to be neither rare nor typical only of lesser-studied languages with unstable grammatical organization, as previously assumed. The book also offers an explicit discussion on the non-existence of phonological affix ordering, with a focus on mobile affixation, and one on the emergence of affix ordering in child language, the first of its kind in the literature. Repetitive operations, undesirable in many theories, are frequent in early child language and seem to serve as trainings for morphological decomposition and affix stacking. Thus, the volume also raises important questions regarding the general architecture of grammar and the nature and side effects of our theoretical assumptions.