How to open Nautilus (File Manager) preferences?

On Ubuntu 17.10.1, the top left corner of the screen next to Activities, you'll find Files with a drop-down arrow:

Click on Files, then in the list that appears, click on Preferences.

For Gnome

It appears that you made an ill-advised change with the Tweak-tool in Gnome. gnome-tweak-tool is available for all currently supported versions of Ubuntu and is readily installable by activating the Universe repository and installing it via Software Center or via the command line with sudo apt-get update&&apt-get install gnome-tweak-tool

Open it (via terminal if necessary with gnome-tweak-tool Navigate to Top Bar and flip "Show Application Menu" toggle to ON. This will return the Files button to your top bar menu where you can access Preferences.

For Unity or Mate DE's In Ubuntu 14.04 and 16.04 you can simply use the key combination Alte and then n This will open the preferences menu which looks like this:

For Kubuntu (Plasma DE)

AltF3 and "More Actions" Brings up most preferences in Nautilus. If what you are looking for isn't there try the Menu button in the upper right corner of the window.

For Lubuntu (LXDE DE) Not a lot here, Options available from the V button near the upper right corner of the window.

For 18.04, Gnome (for other desktops, see below):

The same as for 17.10 - as seen in the other answer.

When Tweaks tool is used, especially with various extensions, in order to have the above option be sure App Menu is not disabled, including in per-extension settings.

For example, with the Dash to Panel extension, which creates an all-in-one dock/panel (the dock is merged into the panel) and brings the favorite and running applications icons onto the panel, you have a specific settings button under which you can enable/disable App Menu:

But, with the same extension, as App Menu is not really needed anymore, it can be disabled without losing access to the Nautilus settings, as the Nautilus/Files icon that now appears onto the panel (when the program is opened) has the "Preferences" option in the right-click context menu:

The Nautilus settings are also available as gsettings, editable through dconf Editor - as already indicated by this answer - at the level org.gnome.nautilus.preferences:

Outside Gmome, namely in Ubuntu Budgie, the left-corner button that gives access to those options (but which is missing in Ubuntu 18.04 Gnome) is not missing with the same version of Nautilus 3.26.3.

I got the same question on Xenial (16.04) but none of the other answers worked for me.

I found that you can edit nautilus preferences with the dconf-editor tool. The offending section is in org.gnome.nautilus.preferences.

Unfortunately, some options may not be editable (that was my case with a drop-down list that was not allowing correct keys). In that case, you may use the following command: gsettings org.gnome.nautilus.preferences <KEY> <VALUE>.