Happiness is a mental or emotional state of well-being characterized by positive or pleasant emotions ranging from contentment to intense joy. A variety of biological, psychological, religious, and philosophical approaches have striven to define happiness and identify its sources.

Various research groups, including Positive psychology, endeavor to apply the scientific method to answer questions about what "happiness" is, and how we might attain it.

Philosophers and religious thinkers often define happiness in terms of living a good life, or flourishing, rather than simply as an emotion. Happiness in this sense was used to translate the Greek Eudaimonia, and is still used in virtue ethics.

Happiness economics suggests that measures of public happiness should be used to supplement more traditional economic measures when evaluating the success of public policy.

Happiness is a fuzzy concept and can mean many things to many people. Part of the challenge of a science of happiness is to identify different concepts of happiness, and where applicable, split them into their components.