No class of words has better claims to universality than interjections. At the same time, no category has more variable content than this one, traditionally the catch-all basket for linguistic items that bear a complicated relation to sentential syntax. Interjections are a mirror reflecting methodological and theoretical assumptions more than a coherent linguistic category that affords unitary treatment. This chapter focuses on linguistic items that typically function as free-standing utterances, and on some of the conceptual, methodological, and theoretical questions generated by such items. A key move is to study these items in the setting of conversational sequences, rather than from the “flatland” of sequential syntax. This makes visible how some of the most frequent interjections streamline everyday language use and scaffold complex language. Approaching interjections in terms of their sequential positions and interactional functions has the potential to reveal and explain patterns of universality and diversity in interjections.