As stated in https://www.zotero.org/support/kb/sentence_casing , Zotero assumes that titles stored in its own database are in sentence case. When exported to BibTeX, words with uppercase letters in titles are protected in curly braces. For example, an article title "Grandmaster level in StarCraft II using multi-agent reinforcement learning" is transformed to "Grandmaster level in {StarCraft} {II} using multi-agent reinforcement learning" with BibTeX exporter. However, BibTeX only provides a function that transforms to sentence case but not vice versa. In order to work with most BibTeX styles, the .bib database should store titles in title case with proper nouns protected in braces (see https://tex.stackexchange.com/a/140071 ). In the previous example, the correct title in BibTeX .bib file is "Grandmaster Level in {StarCraft} {II} Using Multi-agent Reinforcement Learning". Such transformation is suggested in the BibTeX exporter.