Citations are crucial for intellectual honesty (avoiding plagiarism) and precision.  Quoting requires quotation marks; for three or more authors, use "et al."  Citation formats vary depending on the source.  For articles, cite author name, title, magazine title, date, volume, issue, and page numbers.  For books, cite author name, title, place of publication, publisher, and year. Websites require author, year, page title, site title, URL, and access date. Master's theses need author, year, title, university, and access details.  Thesis citations include author, title, thesis type, discipline, institution, year, and page count. Over 2000 citation styles exist, with MLA and APA being popular.  APA style uses (Name, P. (Year). Title. Place, publisher), while MLA uses a "List of Works Cited" with full references at the end. MLA is an author-date system used mainly in sciences. Harvard style is exemplified by Mucchielli, L., (2018). Sociology of delinquency. Malakoff: Armand Colin. Citation systems include notes and bibliography (preferred in humanities) and author-date (common in sciences and social sciences).  Chicago style uses numbered footnotes or endnotes (notes and bibliography) or author-date system.  An example is Einstein, Albert. La signification de la relativité. Princeton: Princeton University Press, 1923.