The IB does not require the use of any one style guide for citations and notes, only that the writer consistently follow one style throughout the essay. The following websites provide guidance to the most commonly used citation styles:
MLA: Modern Language Association: for the humanities, art, and literature. 7th ed., 2009:
https://owl.english.purdue.edu/owl/resource/747/01
Chicago Manual of Style: used for all subjects. 16th ed., 2010:https://owl.english.purdue.edu/owl/resource/717/01/
Turabian: A derivation of Chicago, for any subject but intended for history. 7th ed., 2007: http://www.library.georgetown.edu/tutorials/research-guides/turabian-footnote-guide
AMA: American Medical Association: used most for medicine, health, and biological studies. 10th ed., 2012: see http://www.lib.jmu.edu/citation/amaguide.pdf
APA: American Psychological Association: used most for psychology, education and social sciences.6th ed., 2nd printing: see http://owl.english.purdue.edu/owl/resource/560/01/