updated April 13th, 2019.

ENBSeries is a graphical modification for many games, including Skyrim. It uses a modified d3d11.dll file, implementing new graphical options such as ambient occlusion, indirect lighting, Bokeh depth-of-field, lens effects, better bloom, HDR, tone maping, parallax maping, vignette, sun rays, detailed shadows, film grain, reflections and much more to come in later versions.
The settings can be modified and adjusted to your liking. Many people have released their own ENB presets which they use and wish to share.
And no, the creator won't tell us what the ENB name actually means.  I'm serious, he won't. Don't attempt to figure out what it stands for and just remember what it does; it makes your games look pretty. Go to the official website for more information.

How do I use ENB?

First, you want to get the d3d11.dll file from the official website. Usually the newest release is the best option, but some presets require a specific version because of stabilization or specific issues. After downloading the enb, place the files into the Skyrim main folder (usuallly Steam\steamapps\common\Skyrim Special Edition\). Now if you want to use a preset made by someone else, download and extract it to the same place as before. This should overwrite some files but it shouldn't interfere with the d3d11.dll. Once you start the game, you should see a significant difference between the ENB and vanilla.

What's the best ENB to use?

Here are a few examples of ENB in-game.
Please note that performance will depend on what binary version the ENB is and what kind of computer you have. This varies depending on your processing speed, how much RAM you can allocate, and what kind of graphics card you have.
ENB SE no longer manages the memory allocation for Skyrim, making its needs mostly aesthetics now with just a couple of fixes like disbabling fake lights.
Also, with Boris constantly updating ENB SE, more and more Legendary Edition ENBs are starting to work with SE, if you do not find a good ENB here, try the ones on the Legendary Edition page, they might just work. (Thanks Todd.)
There really isn't a "best ENB" out there.  It all comes down to player preference, or how well your rig can handle that specific ENB preset. You gotta search for what you like.  You can use a really colorful ENB, or a very movie-esque preset with film grain and filters, or even a very simplistic one with just SSAO and a few lighting tweaks.  Here are a few ENB presets that we would recommend to you. An ENB could also have optional presets for low and high end computers. Some features would be removed or added depending on the settings but will accommodate you better.  Check out the UESP link for full details on the specs. You should never use an ENB if you don't meet the game's minimum requirements, even if it is a really simple ENB. If you can run the game at Ultra settings with no issues with textures, than you're pretty much set you use anything you want!
Click on the pictures to go to the ENB links!

What is Reshade?

Reshade is a post processing tools that tweak and add new features to almost any game, including Skyrim.
They improves anti-aliasing, bloom, HDR, tonemapping, and even adds new features such as LumaSharpen, Technicplor, Cineon DPX, and more. It also works with ENB, so you can use both at the same time. Some ENB presets come with SweetFX now for easy installation.


Q: What is lacking on ENB SE?
A:  ̶M̶o̶s̶t̶ ̶s̶h̶a̶d̶e̶r̶s̶,̶ ̶a̶s̶ ̶t̶h̶e̶y̶ ̶n̶e̶e̶d̶ ̶t̶o̶ ̶b̶e̶ ̶r̶e̶m̶a̶d̶e̶ ̶f̶r̶o̶m̶ ̶t̶h̶e̶ ̶g̶r̶o̶u̶n̶d̶ ̶u̶p̶ ̶t̶o̶ ̶w̶o̶r̶k̶ ̶w̶i̶t̶h̶ ̶S̶p̶e̶c̶i̶a̶l̶ ̶E̶d̶i̶t̶i̶o̶n̶,̶ ̶t̶h̶e̶ ̶E̶N̶B̶ ̶d̶e̶v̶ ̶i̶s̶ ̶s̶l̶o̶w̶l̶y̶ ̶a̶d̶d̶i̶n̶g̶ ̶t̶h̶e̶m̶ ̶b̶a̶c̶k̶ ̶i̶n̶.̶  A lot of shaders have been added, a couple are still missing.
Q: I only see the wrapper in the ENB package, where is the injector?
A: Gone.
Q: What does it mean when an ENB says it's incompatible with a lighting mod?
A: When an ENB says it's incompatible with something like Climates of Tamriel, it really means that the ENB would look different with it on. You can use the ENB with or without certain mods, but the ENB will look a little different than what the auther envisioned because mods like CoT change the brightness and saturation of the base game.  This will also change how the ENB will look like in the end. Most ENBs now come with various compatibility versions for different weather mods.
Q: Why does my game keep crashing when I have ENB and SweetFX on at the same time?
A: It's probably because you need more VRAM. ENB and SweetFX are both post processing programs that go over your game which makes the game look different to the viewer and doesn't necessarily edit the game. This will take a toll on any PCs because of the amount of VRAM required to keep up the post processing and filters at a steady pace.  So in this case, you'll have a layer of post processing over post processing. To remedy this issue, try enabling only a few of each setting on both ENB and SweetFX to have a perfect combination of the two that won't set your computer on fire. 
Q: Which ENB file controls the DOF effect?
A: That would be the "enbeffectprepass.fx" file.  It should come packed with any ENB preset.