Studies of laughter are spread over multiple scientific disciplines of which many have nothing or nearly nothing in common: from conversational analysis and interactional linguistics to emotional psychology, from phonetics and speech technology to physiology, from evolutionary biology to cultural studies. Laughter and humor are frequently used synonymously. Laughter is a salient acoustic behavior in everyday communicative situation, there are comparably few studies on its acoustics, perception, and physiology. Laughter is often seen as an expression of emotion and linked to positive feelings. Laughter seems to mainly fulfill a social function. The phylogenetic origin of smiling is often referred to the silent bared-teeth display, whereas the relaxed open-mouth display is also known as play face. Laughter is a non-verbal phonetic activity that usually occurs in conversational interaction with an interlocutor. It was stressed that laughter usually occurs in spoken interaction and that the social dimension is also reflected in common or shared laughter.