This book researches the various ways of saying 'yes' and 'no' in Welsh. In many languages, responding with 'yes' or 'no' is simple. This work shows that in Welsh a variety of forms can be used, depending upon syntax, morphology, lexis and semantics. The opening chapter considers data from a number of languages to establish a typology of answering systems which allows the main features of the Welsh system to be introduced. Further chapters present descriptive analyses of the forms of Welsh responsives, the influences which determine their appropriate use, and their discourse functions. Another chapter provides a formalized analysis of the main descriptive details. The descriptive and formal analyses are exploited in the remaining chapters to show how young children from different language backgrounds cope with a complex system of rules. To this end, the work researches an extensive corpus of children's spoken Welsh, achieved with the aid of the programming language Icon. The study reveals the nature of variation in young children's use of 'yes' and 'no' forms, and quantifies the extent of the variation with statistical analyses which are produced with the computer package Minitab. Two main causes of variation are discussed: language contact as facilitated through bilingualism, and internal influences involving isomorphism, discourse functions, and semantics. The analyses are copiously illustrated with examples; figures and regular summaries help to present the discussion; and tables are provided in support of the statistical analyses. Overall, the work will appeal to scholars of various interests: the chapters which analyse the answering system provide interesting data for theorists and comparative linguists; the chapters which describe and attempt to explain variation will be of interest to sociolinguists; and, of course, the whole work will appeal to Celticists. About the author: Bob Morris Jones is a Senior Research Associate at the Department of Education, University of Wales, Aberystwyth.