Emotions play a central role in our lives, but their definition is not straightforward and there is no consensus opinion as to what exactly they are.
Understanding emotions is important because they are a crucial factor in decision-making. Emotional learning is also important in shaping personality. Emotions play a significant part in mental illness, most obviously in anxiety disorders but also in personality disorders such as psychopathy and borderline (emotionally unstable) personality disorders, as well as in schizophrenia.
The study of emotions has a long history in the field of psychology and early contributions were made by Darwin, Freud and William James. Research into emotions has produced some famous theories and seminal experiments which are still a matter of debate today; much of this debate revolves around the contribution and relationship between the biological (or physiological) and cognitive parts of the emotional response.