Fillers are items that speakers insert in spontaneous speech as a repair strategy. Types of fillers include hesitation markers and placeholders. Both are used to fill pauses that arise during planning problems or in lexical retrieval failure. However, while hesitation markers may not bear any resemblance to lexical items they replace, placeholders typically share some morphosyntactic properties with the target form. Additionally, fillers can function as a pragmatic tool, in order to replace lexical items that the speaker wants to avoid mentioning for some reason. The present volume is the first collection on the topic of fillers. It consists of typological surveys and in-depth studies exploring the form and use of fillers across languages and sections of different populations, including cognitively impaired speakers.