Quantifying happiness isn't an easy task. Researchers at the Gallup World Poll went about it by surveying thousands of respondents in 155 countries, between 2005 and 2009, in order to measure two types of well-being. First they asked subjects to reflect on their overall satisfaction with their lives, and ranked their answers using a "life evaluation" score from 1 to 10. Then they asked questions about how each subject had felt the previous day. Those answers allowed researchers to score their "daily experiences"--things like whether they felt well-rested, respected, free of pain and intellectually engaged. Subjects that reported high scores were considered "thriving." The percentage of thriving individuals in each country determined our rankings.