Harvard is a parenthetical author-date reference system. Harvard reference style originates from Harvard University, where a professor of zoology in the 1880s first used parenthetical references.
What is Harvard style?
Most reference styles are based on manuals published by scholarly associations or by publishing companies. This is not the case with Harvard, and, consequently, there are not one but several versions of Harvard style. The differences between the different versions are small and mainly concern the use of punctuation.
When guidelines within the same reference style differ, as is the case with Harvard, it is important to pay attention to consistency. This means that although the use of punctuation may differ between style manuals, writers must always be consistent within their texts.