Hi Chihiro! The rules vary depending on the context. For example, let's say you are writing an essay and want to reference the source of your information. For complete bodies of work such as books or newspapers, you will italicize the letters. If you are referencing a shorter work such as an article, journal, poem, or short story, you will put the title in quotation marks. If you are titling an original body of work that you wrote, the rules are different. You do not need to italicize or use quotation marks. Document titles are usually written in all upper case or title case. Title case capitalizes the principal words of importance and leaves prepositions, articles, and conjunctions in lowercase. However, the first word of the title is always capitalized even if it is not a principal word. For example: 500 Days of Summer Eternal Sunshine of the Spotless Mind And Still I Rise The Curious Incident of the Dog in the Night-Time The Hotel on the Corner of Bitter and Sweet (notice how "and" is not capitalized unless it starts the title) I hope this helps!