First, please make sure your system meets the minimum requirements for the game. Check the System Requirements on Subnautica's Steam store page. Subnautica is a modern 3D game with beautiful graphics and therefore requires a 64bit machine, a good graphics card, and lot of RAM.
Video Card Drivers
Please make sure your video card drivers are up to date. Sometimes Unity3D fails to select your best graphics card if you have more than one. Usually updating your graphics card drivers or creating a profile for Subnautica in your graphics driver's control center helps.
Here are the links to various graphics card drivers by manufacturer: Nvidia GeForce[www.geforce.com], other Nvidia cards[www.nvidia.com], AMD/ATI cards[support.amd.com], and Intel HD Graphics[downloadcenter.intel.com]. Steam can also help you search for the latest drivers. In the Steam menu navigate to Check for Video Driver Updates... and let Steam guide you through the process.
Sound Card Drivers
Subnautica uses the FMOD audio libraries. Unfortunately FMOD crashes if the sound card is not installed properly. A good indication of a sound driver issue is when it crashes before the main menu shows up.
Please try to find a sound card driver update on the vendor's site. Common vendors are RealTek[www.realtek.com.tw] and C-Media[www.cmedia.com.tw]. You should be able to find information about the sound card vendor in the Windows Device Manager.
Additionally there are sound issues with Windows 10. These are not related to Subnautica but will prevent the game from starting. Please follow these instructions from Microsoft to fix sound driver issues in Windows 10.
Subnautica is built using the Unity3D[unity3d.com] engine. Most issues with hardware, configuration, or outdated drivers are not unique to playing Subnautica. It is generally preferable if you have all the latest drivers installed for your hardware, especially video and audio drivers. See if anything shows up in Windows Update.
Surprisingly often Steam fails to install or update Subnautica correctly. We don't know why but we know it happens. If Subnautica's installation is broken all bets are off and the weirdest bugs can happen. To make sure your installation is fine right click Subnautica in Steam and select Properties. Then navigate to Local Files and click the Verify Integrity of Game Cache button. In rare cases the installation might be broken even though all files pass the validation. In that case all you can do is uninstall and re-install the game. Please verify the cache integrity after re-installing. Also verify the cache integrity after every update to the game. Did I mention verifying the cache integrity already? It helps.
If your graphics card does not support Direct3D 11 or you experience other issues related to the looks of game you can try running Subnautica on Direct3D 9. To do so right click Subnautica in Steam and select Properties. Navigate to the General tab and click the Set Launch Options... button. Enter -force-d3d9. Note the leading dash.
That said, this option should be seen as a last resort. Subnautica runs fine using D3D11 on all graphics cards that meet the minimum system requirements. If for some reason D3D9 fixes anything for you what you really want to do is update your drivers and your Windows. See above.
You may also experience crashing at launch of Subnautica. It is possible your sound frequency settings may need to be reset. In Windows Vista and 7, go to your Control Panel and Open Sound. In Windows 8, 8.1 and 10, press the Windows key, search for sound, and Open up the Sound Control Panel.
Scroll and find your Default Sound Device (it's usually the green ticked one) in the Playback tab. For Realtek or other sound chip users, it will display that brand. Click on it to highlight it, then click Properties.
Open the Advanced tab on the top right of the Window. Then in the drop-down select 24 bit, 44100 Hz (Studio Quality) then hit Apply and OK.
Click OK on all the dialog boxes. You may have to restart your PC for the settings to take hold. Launch Subnautica and see if it runs OK.
Mac OSX Issues
There are a few known issues currently with MacOS X and Subnautica / Unity in general.
If you are having issues with using your 1-5 keys and you are using a AZERTY or non-QWERTY Keyboard on your Mac, you will need to switch your keyboard layout to QWERTY[support.apple.com]. You can always switch it back. This is a Unity engine issue and has been reported. It does not affect Windows users.
When playing Subnautica on a Mac in Full Screen mode, you may find you have a green background. You can work around this by playing in a window. Click the Full Screen check box in the options menu to enable/disable full screen until the water background shows.
Game hangs while loading
If the game just hangs while loading the game please be patient. The same thing happens for a couple of people, especially after updates. On most machines it takes about one minute to load the game but for some people it takes much longer. So if the game goes white on the loading image with the burning space ship please just sit there and wait. Leave it as white, don't click any box that comes up, wait for about five minutes, and see if the game comes back. It almost always does. Make sure to verify the cache integrity if it doesn't. See above.
Game crashes while playing
We are aware of the fact that on some machines Subnautica crashes after running for a couple of minutes or hours. Of course we want to improve the situation but there can be many potential causes and some of them are outside of our control. Most common issues are: not meeting the minimum system requirements, outdated drivers, running out of memory, and overheating.
So please do your part. Check your system specification, update your drivers, close all other applications, and provide good ventilation. It goes a long way.
Two other potential sources for crashing are bugs in the Unity3D game engine we are using and bugs in our shader code. We are integrating Unity's bugfixes as soon as they are available and we keep improving our shader code.
Mouse pointer offset
There is an issue with the current build where mouse clicks would not appear at the same position where the mouse pointer is. For example you might want to click New Game but you hit Options instead. Or you can not use the Fabricator menu anymore because your clicks will not hit the icons.
If you are experiencing anything like that it means you are running the game in fullscreen on a resolution with a different aspect ratio than your monitor. Playing in Windowed mode or selecting a resolution native to your monitor will fix the problem.
Subnautica is available in many languages. The translations are entirely community driven! If you find your language support to be incomplete feel free to help by providing feedback in the translation forum[forums.unknownworlds.com] or by adding/upvoting some translations at http://translate.unknownworlds.com/. Thank you!
In-Game Feedback System
The easiest way to report issues encountered within the game is to use the in-game feedback system. To use it, press F8 while in game. Subnautica will pause and a feedback panel will appear. The feedback panel gives you a bunch of options for sending information to the development team. Marking feedback as a bug, a performance problem, a gameplay problem or some other category helps the team sort and prioritize reports. See the Development Feedback guide for details. http://steamcommunity.com/sharedfiles/filedetails/?id=356376081
Ask for help
If all of the above does not help, or you have other random issues, try asking for help on our Subnautica forums[forums.unknownworlds.com]. We have a very dedicated community experienced in tech support. Please make sure to include a short description of the issue to speed up the process. It helps to be as precise as possible about the issue you encounter. Make sure to attach the log file in case of crashing.
Subnautica is not finished yet. Being in Early Access means that it is changing and morphing all the time. The Development Updates guide explains how to find out what the development team is doing, how you can tell them what you think, when you can expect updates, and how to get them. http://steamcommunity.com//sharedfiles/filedetails/?id=355026171