Influential approaches to the definition and operationalization of beliefs and other affective dimensions are described in this chapter. Snapshots of research findings are presented, commonly used measures are listed, and some technologically enhanced approaches to the measurement of beliefs and affect are discussed. Contributions, both theoretical and practical, to research on the affective domain by those concerned with gender issues are also referenced. Keywords Affect • Beliefs • Gender • Mathematics • Measuring affect 2.1 About Beliefs, Affect, and Mathematics-Introduction 2.1.1 Setting the Context Why, it could be asked, are both beliefs and affect in the title of this contribution? The inclusion of both terms warrants a special comment. In his influential and frequently cited article Pajares (1992) argued convincingly that, within the field of educational psychology, defining beliefs is at best a game of player's choice. They travel in disguise and often under alias-attitudes, values, judgments, axioms, opinions, ideology, perceptions, conceptions, conceptual systems, preconceptions, dispositions, implicit theories, explicit theories, personal theories, internal mental processes, action strategies, rules of practice, practical principles, perspectives, repertories of understanding, and social strategy, to name but a few that can be found in the literature. (p. 309) Mason (2004) similarly argued that it is often difficult to work out what beliefs actually cover and illustrated this by producing "an entire alphabet of associated interlinked terms":