The style-guide gurus don't always agree on how to capitalize. This lesson will show you the rules for the most widely-used styles.
Source: Linda Neuman, http://employees.csbsju.edu/proske/nursing/APA.htm#bkex1, http://owl.english.purdue.edu/owl/resource/747/05/, http://grammar.about.com/od/grammarfaq/f/capitalstitle.htm