ToUpperCase[string] yields a string in which all letters have been converted to upper case.
ToUpperCase handles both ordinary and special characters.
Variant lower-case characters such as \[CurlyPhi] are converted to their non-variant upper-case forms.
See The Mathematica Book: Section 2.7.4.
See also: UpperCaseQ, ToLowerCase, StringReplace, IgnoreCase.