The authordate3 BibTeX style generates citations in the author-date citation system also known as Harvard referencing. In this style the casing of titles of articles, journals and books is not changed. Author's and editor's names are in small capitals.
\documentclass[a4paper,10pt]{article}
natbib
\begin{document}
This is an example of a paragraph with in-text
citations using the authordate3 BibTeX style.
Here is a reference to a journal article with
a single author \cite{article1}, to a journal
article with two authors \cite{article2} and
three authors \cite{article3}, and to a book
with four authors \cite{book4}.
\bibliographystyle{authordate3}
\bibliography{sampleBibFile}
\end{document}