We examine clarification dialogue, a mechanism for refining user questions with follow-up questions, in the context of open domain Question Answering systems. We develop an algorithm for clarification dialogue recognition through the analysis of collected data on clarification dialogues and examine the importance of clarification dialogue recognition for question answering. The algorithm is evaluated and shown to successfully recognize the occurrence of clarification dialogue in the majority of cases and to simplify the task of answer retrieval. 1 Clarification dialogues in Question Answering Question Answering Systems aim to determine an answer to a question by searching for a response in a collection of documents (see Voorhees 2002 for an overview of current systems). In order to achieve this (see for example Harabagiu et al. 2002), systems narrow down the search by using information retrieval techniques to select a subset of documents, or paragraphs within documents, containing key...