Nogizaka Haruka no Himitsu

is a Japanese light novel series by Yūsaku Igarashi, with illustrations by Shaa. The series originally started serialization in MediaWorks' now-defunct light novel magazine Dengeki hp on June 18, 2004. The first novel was released in October 2004, and as of January 2012, 15 volumes have been published by ASCII Media Works under their Dengeki Bunko imprint.