The World Happiness Report measures "subjective well-being" - how happy people feel they are, and why.
Nordic countries regularly appear in the top five, while war-hit countries and a number in sub-Saharan Africa regularly appear in the bottom five.
Burundi was the least happy, taking over from the Central African Republic.
It was thrown into crisis when President Pierre Nkurunziza's bid for re-election to a third term in 2015 sparked protests by opposition supporters who said the move was unconstitutional.
This year's report by the UN Sustainable Development Solutions Network also features data about the happiness of immigrants in their host countries, with Finland also coming top as home to the happiest immigrants