Baseline (Widescreen) Solution & Issues
0 A.D. runs at the desktop resolution by default. Widescreen resolutions are detected automatically and everything has the correct aspect ratio.
There are no resolution options in-game; other resolutions can be set by adding -xres= and -yres= shortcut parameters to the end of the shortcut target, e.g. to set 1280x720 you would use -xres=1280 -yres=720.
Resolutions can also be set by going to the user folder in the game data path and making a file called user.cfg containing the following two lines:
xres = 1280
yres = 720
Adjust the numbers to match the resolution you want.
Ultra-Widescreen (21:9) Specific Solution & Issues
Eyefinity / Surround Specific Solution & Issues
4k UHD Specific Solution & Issues
Stereoscopic-3D Solution & Issues