Some citation styles, such as APA, require the use of sentence case for titles (e.g., “Oxidation and reduction of iron by acidophilic bacteria”). Others, like the Chicago Manual of Style, require title case (“Oxidation and Reduction of Iron by Acidophilic Bacteria”).

Unfortunately, it's not possible for Zotero or any other tool to reliably automate conversion to sentence case, since a computer can't know for sure that something is a proper noun. (Think, for example, of the word “united”, which can be an adjective, verb, name of a company, or part of a country name.)

The solution is to store titles in sentence case in your Zotero library and let Zotero automate the conversion to title case if necessary. For example, when using Chicago Manual of Style, Zotero will automatically convert titles to title case, whereas when using APA it won't try to enforce sentence casing and will simply print titles as they appear in your library.

If you find that a title is incorrectly showing in title case in your bibliography, make sure that it is stored in sentence case in your Zotero library. You can automate part of the conversion into sentence case by right-clicking on the unselected title in the Info pane and choosing “Sentence case”. You will then need to manually capitalize any proper nouns. You only need to do this once, and then Zotero will always use the correct case for that item, no matter what citation style you're using.

It is also possible to prevent title casing of non-English titles.

Some styles that require sentence case, such as APA, also require that the first letter of the subtitle following a colon also be uppercase (“Age and environmental sustainability: A meta-analysis”). Zotero will automatically capitalize the subtitle for styles that require it. If the title contains multiple colons or dashes, store the main title (before the colon) in the Short Title field to indicate where the subtitle begins.