Influential theories on affect and emotion propose a fundamental differentiation between emotion and cognition, and research paradigms designed to test them focus on differences rather than similarities between affective and cognitive processes. This research orientation is increasingly challenged by the widespread and successful use of cognitive research paradigms in the study of affect and emotion - a challenge with far-reaching implications. Where and on what basis do theorists draw the line between cognition and emotion, and when is it useful to do so? Should researchers build more global, integrative models of cognition and emotion, or should they rely on local, content-specific models that draw attention to a differentiation between affective and cognitive processes? This special issue compiles different viewpoints on fundamental issues in the relationship between affect and cognition.