This guidance applies whether you found the treaty in print or online.
legislation title | [year] | OJ series | issue/first page
Footnote and bibliography:
e.g. Consolidated Version of the Treaty on European Union  OJ C115/13
To pinpoint, follow the citation with a comma, the relevant term or abbreviation and a number or letter. To pinpoint several articles (for example), insert a dash between the article numbers:
e.g. Consolidated Version of the Treaty on European Union  OJ C115/13, art 2
The year is always given in [square brackets].
The main source for EU legislation is the Official Journal of the European Union (OJ), which comprises two series:
Older treaties were published in the C series. Most legislation is now published in the L series (with the exception of the Lisbon Treaty).