Harvard System of Referencing was created in 1881, actively introduced at the beginning of the 20th century and is most common in biomedical research works. Harvard citation style belongs to “author-date“ system. There are several versions of Harvard citation style (Harvard, Harvard-British Standard, Harvard-British Standard 2010, Harvard Business Review, Harvard Theological Review (Author-Date), Harvard Theological Review (Notes-Bibliography)). Most often citation style versions are chosen according science fields and regions (e.g. Harvard-British Standard is used in works by scientists from Great Britain).