Underscored first letter ...

Why are the first letter of right-click menu options sometimes underlined?

Is there some sort of keyboard shortcut in conjunction with the underlined first letter?

Alt- plus that key.

Not sure about right click menus, but pull-down menus in Windows do sometimes have this convention. To activate one of them menus, for example File, one hits ALT + Underlined letter. Then, if there is an option in the menu such as Save, one can just hit the letter.

It is a way to use the pull down menu from the keyboard, without the use of a mouse.

On a popup menu, you don’t need the alt. In fact, alt will make the popup disappear. For instance, right click to bring up the context menu on this page, and simply press “m” to bookmark it (I’m using firefox).

Almost, but I think the above answers are just slightly wrong.

In pop-up and drop-down menus, many items will have some letter underlined (not necessarily the first letter). While the menu is open, you just type THAT LETTER BY ITSELF of activate that menu option. Don’t press either Alt or Ctrl, as doing so will just cause the menu to close. Type the letter by itself.

This is for drop-down menus. I THINK context menus (right-click menus) work the same way.

The items on the main menu bar at the top of the window work differently. For these, you type Alt and the underlined letter.

In forms, where you have a caption next to a text box, checkbox, radio button, or on a click button, it’s Alt plus the underlined letter.

Not sure what the rules are on a Mac.

ETA: Partly ninjaed by yabob

BTW, the seeming inconsistency is a matter of whether the menu control you are using the keyboard accelerator on has focus or not. You don’t actually have to press alt and the keyboard accelerator together for the top menu. If you press and release “alt”, you will notice it focuses on the top menu. You can then press the accelerator key for your menu choice, or navigate to the one you want with the arrow keys and press enter.