This book edition highlights recent trends and important issues that still remain only partially solved or even unsolved within the broad ?eld of discourse and dialogue. The ?eld is discussed and illustrated both from an overall spoken (multimodal) dialogue system perspective as well as from a more compone- related perspective. Issues discussed include, for example, discourse and dialogue modelling in research versus industrial spoken dialogue systems, evaluation, miscommunication and error handling, grounding, statistical and corpus-based approaches to discourse and dialogue modelling, data analysis, and corpus annotation and annotation tools. We believe that jointly this collection of chapters provides a good picture of how far we are today within discourse and dialogue and of important ch- lenges ahead. On this background we hope that computer scientists, engineers, and others who work in the broad area of discourse and dialogue, no matter if from an academic or industrial perspective, may bene?t from the book and ?nd it useful to their own work. Graduate students and Ph.D. students focusing on topics in discourse and dialogue may also ?nd the book interesting and pro?t from reading it. This book edition is based on a selected subset of papers from the successful 6th SIGdial Workshop on Discourse and Dialogue held in Lisbon, Portugal, in September 2005 in conjunction with the 9th Eurospeech (Interspeech) conf- ence. SIGdial is a special interest group on discourse and dialogue sponsored jointly by the two parent organisations ACL (Association for Computational Linguistics) and ISCA (International Speech Communication Association).