The base of the entire Hetalia series is its Manga.
The art and story belongs to Hidekaz Himaruya, and is originally in Japanese. Other countries have obtained the rights to translate the manga, and retail values vary depending on publishers.
Currently, four volumes exist, and a fifth has been mentioned by the artist, though progress on it is unknown.
Hetalia has also started serialization in Comic Birz.
The original Japanese releases come in two versions: Regular, retailing at 1050円 ($14) per copy, and Limited Edition, 1260円 ($16.80).
Volume 1 was released on March 28, 2008.
Volume 2 was released December 10, 2008.
Volume 3 was released May 21, 2010.
Volume 4 was released June 30, 2011.