MSSTYLES is a Microsoft file format, that contains the bitmaps and metadata for the Windows XP skinning engine, first introduced in Windows Whistler Build 2250.

The engine in an unmodified state, only fully applies.the msstyles files that have been digitally signed by Microsoft, such as the Moon or the theme of the Zune software. By default Windows XP style is known as Luna, but additional custom presets available on the Internet nevertheless, a few are signed. Four other signed styles for Windows XP can Royale media center edition energy blue, Royale Noir, Windows embedded standard CTP refresh, and the Zune style.

Unsigned styles can be used using different methods, by correcting or manually replacing system files or automatically using one of the programs made for this purpose. These programs are usually called "UxTheme patching" on behalf of the library XP, which requires patching, UxTheme.dll despite the fact that recent versions of Windows require patches to different files. A popular and freely distributed patching can be found online, often use various methods to enable custom themes.

In Windows Vista and later use.msstyles files for skinning as Aero.the msstyles file, but the format of these files will differ, so.the msstyles file cannot be transferred between Windows Vista and Windows XP. This version.the msstyles file contains png images and metadata.

There is a manual way to replace three dll files uxtheme.dll, shsvcs.dll and themeui.dll use unsigned custom visual styles in Windows Vista.