Negation is a universal component of human language; polarity sensitivity (i.e., lexical distributional constraints in relation to negation) is arguably so while being pervasive across languages. Negation has long been a field of inquiry in psychological theories and experiments of reasoning, which inspired many follow-up studies of negation and negation-related phenomena in psycholinguistics. In generative theoretical linguistics, negation and polarity sensitivity have been extensively studied, as the related phenomena are situated at the interfaces of syntax, semantics and pragmatics, and are thus extremely revealing about the architecture of grammar. With the now long tradition of research on negation and polarity in psychology and psycholinguistics, and the emerging field of experimental semantics and pragmatics, a multitude of interests and experimental paradigms have emerged which call for re-evaluations and further development and integration. This special issue contains a collection of 16 research articles on the processing of negation and negation-related phenomena including polarity items, questions, conditionals, and irony, using a combination of behavioral (e.g., rating, reading, eye-tracking and sentence completion) and neuroimaging techniques (e.g., EEG). They showcase the processing of negation and polarity with or without context, in various languages and across different populations (adults, typically developing and ADHD children). The integration of multiple theoretical and empirical perspectives in this collection provides new insights, methodological advances and directions for future research.