Hiding in D&D 5E

Hiding is poorly explained and/or poorly understood. Here's my take on it.

Summary

If something is "unseen" then you can't see it but you probably know where it is. If it is "hidden" then you can't see, hear or smell it and you might not even know it is there at all.

Unseen

You can't see the thing. You may or may not know the thing is present, depending on its noise or smell or on signs of its passage.

It has not taken any steps to hide its presence. If it had, it would be Hiding (see below).

How does a thing become Unseen?

There are many game effects that can cause a thing to become Unseen but they generally fall into one of two effects - concealment and lack of light.

Concealment is when there is something between you and the thing. For example: mist, foliage, smoke, squid ink, magical darkness.

Lack of light is when there is nothing between you and the thing but there still isn't any light illuminating it. Usually this when the thing is in an area of mundane darkness. It is also caused by you having the blinded condition.

How do I know where an Unseen thing is?

You know roughly where it is (on a grid, you know its square/hex) because you can hear it or smell it or see its footprints or perceive its location in some other way.

Can I attack an Unseen thing? Can it attack me?

Yes and yes.

If you cannot see it and it can see you then you have Disadvantage on your attacks.

If it cannot see you and you can see it then you have Advantage on your attacks.

If neither of you can see the other then you both attack normally (the Advantage and Disadvantage cancel, though other sources of Advantage/Disadvantage might still apply).

But… You can't target it with any attack or spell or feature that includes "that you can see" in its targeting. Note that this includes attacks of opportunity.

Hidden

Someone has actively taken steps to conceal the thing's presence.

You don't know where the thing is. You probably don't even know the thing is there at all.

Creatures conceal their own presence by one or more of: Walking quietly and not causing signs of passage. Muffling clothing and gear. Breathing quietly. Masking scent (by walking downwind, for example). Erasing tracks.

Creatures conceal the presence of objects by camouflaging them.

How do I hide a creature?

By telling the GM, "My character attempts to hide" and explaining how theya re going about this. If you are in combat then this will require the Hide Action.

The appropriate Ability Check will probably be DEX\Stealth.

Note that being unseen is required for attempting to hide and remaining hidden. There are exceptions (the Wild Elf racial ability, for example).

Changing location is also usually required. If you duck behind a tree and attempt to hide without moving away then the attempt fails - everyone knows exactly where you are (there she is, behind that tree!).

How do I hide an object?

By telling the GM, "My character attempts to hide the object" and explaining how theya re going about this. Perhaps you are concealing it somewhere. Perhaps you are camouflaging it or disguising it as something else.

The Ability Check required will vary. It will probably be WIS\Survival; but might also be INT\Stealth.

Can I attack a Hidden thing?

Generally, no.

You can guess at a location and blindly attack if you wish, but your chances of landing the hit are low. On top of guessing the location, the thing is Unseen, so the penalties described above will apply.

Use an area-of-effect spell instead. :-)

Can it attack me?

Oh yes! Many classes (Rogue, for example) get great benefit from attacking from hiding.

Attacking from hiding usually breaks stealth. It may or not break unseen.

Can something be hidden but not unseen?

Yes, that's the definition of disguised.

How do I detect an Unseen or Hidden thing?

That depends on the situation. 

Sometimes you will automatically detect it. For example, an Unseen creature walking across snow making sound and leaving footprints.

Sometimes you can never detect it. For example, an invisible statue.

Most of the time it will be a contest between your WIS\Perception and its DEX\Stealth.

If you are trying to deduce its location then you might roll INT\Investigation.

Links

RPG.StackExchange.com: Search

ENWorld.org: A treatise on hiding

ENWorld.org: Why do so many DMs use the wrong rules for invisibility?