What is positive psychological functioning?

Many key theories of human well-being refer to positive psychological functioning, when defining well-being. However, psychological functioning itself is rarely defined and explicated. What exactly do we mean by positive psychological functioning? I review how the term has been used, highlighting a key distinction between subjective well-being, which is about feeling good and positive psychological functioning, which is about the presence of certain key experiential requirements that consistently lead to beneficial psychological and behavioral outcomes. The first tells how the person is doing, the latter focuses on psychological factors that explain why the person is feeling good or bad. I offer a definition and three criteria for elements of positive psychological functioning and propose a distinction between two categories within it: Basic psychological needs as key psychosocial nutriments humans need from their interaction with their environment and basic functional attitudes as ways of approaching life consistently giving rise to well-being.