How To Use Author–Date References (Harvard Referencing)
Parenthetical references usually provide readers with information on the author(s) and publication date of each source cited, and they do so within the main text of a document without any need for the space and formatting required by notes. They therefore constitute an extremely efficient method of referencing and are used by many scholarly authors working in a wide variety of fields.

As a general rule, each author–date reference contains two basic components: the surname of the author (or the surnames of the authors if a source has more than one author) and the publication date of the source cited. Both are usually enclosed within parentheses or round brackets, with the result looking like this: (Smith, 2013), (Smith & Jones, 2015) or (Smith, Jones & Thompson, 2012). Either or both of these components can, however, appear in your main text. If the author’s name is included in the text, the citation would take this form: Smith conducted a similar trial (2013). With the date instead of the author’s name in your main text, the format would be something like this: A similar trial was conducted in 2015 (Smith & Jones). On the other hand, both elements could be included in your running prose, entirely eliminating the need for parentheses: Smith conducted a similar trial in 2013. All of these forms are correct and any one of them can be used in one sentence and a different one in the next. The key to success is ensuring that both the surnames of all authors and the correct publication date are included for each citation.

When parentheses are used for author–date references, it is important to position necessary punctuation marks correctly in relation to the parentheses. This usually means that punctuation marks should follow the closing parenthesis of each reference, just as the full stop follows the parenthetical reference in my next sentence. A more recent investigation of the problem revealed this trend (Smith, 2013). The pattern is the same with other punctuation marks, such as the comma in this example showing a parenthetical reference in the middle of a sentence: According to Smith and Jones (2015), the results were not predictable.

Unfortunately, there is no one style for parenthetical author–date references and there are various differences between the individual styles. For instance, some guidelines and manuals use a comma between the author’s name and the publication date when both components appear in parentheses – (Smith, 2013) – and some do not: (Smith 2013). Some parenthetical references use an ampersand (&) between the last two author names for sources with more than one author, which is the format I have used in the multi-author examples in my first paragraph, while others use the word ‘and’ in that position: (Smith, Jones and Thompson, 2012). However, even when an ampersand is used parenthetically, the word ‘and’ should always be used between author names when they appear in the main text, as it is in the following example: The results obtained by Smith, Jones and Thompson (2012) do not confirm this trend.

Remember that parenthetical author–date references must always be accompanied by an alphabetical list of complete bibliographical references at the end of the document, and that list should include all of the sources cited in your text.