The History Department at WMU requires the use of the Chicago Manual of Style when citing your sources. However, sometimes it permits students to use Kate Turabian's A Manual for Writers of Research Papers, Theses and Dissertations, which is a simplified version of the Chicago Manual. If in doubt--ask your instructor!
The Writing Lab at Purdue University does a superb job of helping to guide students in the use of the writing style guides. Be sure and visit their site once you have put your own citations into the proper format to see check your work.