"Capcom Co., Ltd. (Capcom) is pleased to announce that "Monster Hunter Freedom 3" for the PlayStation®Portable (PSP®) has shipped four million units in Japan. This brings total sales of the "Monster Hunter" series up to 17 million copies."
http://www.capcom.co.jp/ir/english/news/html/e110105.html
It's absolutely stunning how much this series has grown in the space of just a few years.