¿

From Wikislippy

¿ is an upside down ?.

How2

"¿" is available in all keyboard layouts for Spanish-speaking countries.

Windows

On English keyboards under Microsoft Windows, the inverted question mark can be entered by holding down the Alt key and pressing 0191, 168, or 5544 on the number pad. The inverted exclamation point can be entered by holding down the Alt key and pressing 0161, 173 or 8877 on the number pad.

Other

On the Mac OS X platform (or when using the "US International"/us-intl keyboard layout on Windows and Linux), "¡" and "¿" can be entered by pressing Alt (option) + 1 and Shift + Alt (option) + / respectively. With a compose key, for example, <LEFT SHIFT> + <RIGHT CTRL> , they can be entered by pressing the compose key and ! or ? twice.

In LaTeX documents, the "¿" is written as "?`" (question mark, backtick), and "¡" as "!`" (exclamation point, backtick).