E.161 is an ITU-T Recommendation that defines the arrangement of digits, letters, and symbols on telephone keypads and rotary dials.

It also defines the recommended mapping between the basic Latin alphabet and digits (e.g., "DEF" on 3).

E.161 also specifies the dimensions and characteristics of the asterisk and square, referred to in the standard as the 'star' and 'square' keys, respectively.

[a]) The standard also recommends that a tactile identifier be placed on the 5 key to make it easier to use the keypad in low-light conditions or by the visually impaired, as well as multiple alternative methods to implement a recall button.

Language-specific letters (e.g. ü, é, å, ä, ö) as well as other characters (e.g. ‘€’ or ‘@’) are not addressed, which has led to a variety of inconsistent solutions for European languages.