From XnView Wiki
XnView has shortcut keys for most actions that one might want to perform. Many of the keystrokes depend on the mode in which XnView is operating, so the following lists of shortcuts are broken down into three sections, based the display mode: Browser Mode, Viewer Mode, or All Modes (i.e., keys that work the same in both modes).
Moreover, there are some Mouse Shortcuts.
The best way to learn the shortcut keys is simply by looking at the menu option you use to execute an operation; the shortcut key is normally shown on the menu, to the right of the description of the operation. If you frequently create file listings, for example (and this is a really excellent feature of XnView that can be used for many purposes!), you would use the menu Create > File Listing. Note that off to the right of the words "File Listing" the menu shows "Shift+L." That means that the keystoke Shift (holded) plus the "L" key takes you straight to the File Listing function. Experienced users normally prefer the shortcut keys to using the mouse and menus, because it is faster.
Many of XnView's shortcut keys are customizable, meaning that they can be changed by the user. Unfortunately, it is not always easy to find the menu or option where the change can be made. The location of the option is noted in the following sections, where possible. Many of the keyboard/mouse shortcut keys are set in Tools > Options > General > Keyboard/Mouse.
For an in-depth discussion about shortcut keys, and how to extend XnView's shortcut keys, see the XnView forum topic How to change, or/and create new keyboard shortcuts.
Thanks to "Dreamer" for contributing and reviewing the information on shortcut keys; September 2007.