Ask 10 people the question and you'll get 100 different answers. From a baby's laugh to a cute kitten, gardening or a stroll on the beach, we each have a special response to things in life that make us feel happy.
But, what makes you happy way down deep inside? Have you ever tried to figure that out?
Have you ever tried to understand what happened to someone who can't seem to find that happy place in herself?
The Happiness Formula, BBC Two