The upside down question mark ¿
In Spanish, a question opens with ¿ and closes with ?: ¿Cómo estás? The opening mark tells the reader from the first word that the sentence is a question, which matters because Spanish questions often use the same word order as statements. Exclamations work the same way with ¡ and !.
The Royal Spanish Academy recommended the inverted marks in the 18th century, and they are standard in Spanish today. The opening mark goes where the question actually starts, which is not always the start of the sentence: Si llueve, ¿vamos al cine?
Interrobang and other question marks
The interrobang ‽ merges ? and ! into one mark for excited or disbelieving questions ("You did what‽"). Advertising executive Martin Speckter proposed it in 1962. Most people type ?! or !? instead, and those pairs also exist as single characters: ⁈ and ⁉︎. In chess notation, ?? marks a blunder and ?! a dubious move.
The reversed question mark ⸮ was proposed in the 16th century for rhetorical questions and is sometimes used today to signal irony. Other scripts have their own marks: Arabic, Persian and Urdu use the mirrored ؟, and Greek uses a mark that looks exactly like a semicolon (;).
How to type ¿ and ¡
On a Mac, press Option + Shift + / for ¿ and Option + 1 for ¡. On Windows, hold Alt and type 0191 for ¿ or 0161 for ¡ on the number pad (Alt + 168 also gives ¿). On iPhone and Android, press and hold the ? key and slide to ¿. In Word, you can type 00BF and press Alt + X; in HTML, use ¿ and ¡.
The ❓︎ emoji works in chats where you want a bold, colorful question. To flip whole sentences, try the upside down text generator, and for every other mark see the punctuation symbols page.