Nope. No layers. No Xrefs. That's what makes Revit so awesome IMO. I hate layers.

What are you trying to do exactly??

Oh no; you think layers are necessary: forgive me for coming off mean but that's funny...You are fighting it man...

Layers (as you understand them) are no more necessary in Revit than horse-shoes are in a car...

Layers in Revit are more like they are in REALITY; Such as Gypsum Board is a "layer" of a wall, etc... PERIOD!!!

Object characteristics are what they are, independent of any construct like "layer" in ACAD or P-Shop, etc... Objects get Characteristics through paramaterization, Object Styles & their built make-up. That's it... Walls go into the model, not on a walls layer, rather they simply exist in space & time... One can turn on & off, etc. components and sub-components via their category through using Visibility/Graphics (VV) or other less comprehensive means but you will keep banging your head against the wall of ACAD if you keep trying to recreate ACAD processes in Revit WHICH WAS SPECIFICALLY DESIGNED TO BE NOTHING LIKE ACAD!!! ON PURPOSE!!!

Revit is NOT a dumb drafting program, so you may have to get over a lot of built up beliefs for a new way of doing business... One that is more inclined to reality of construction...

great that is no layers all i need is to make external wall on layer and internal wall on the other layers also i need to create layers that i willl call it hidden that i will rely on it to hide temporarily dwg file i imported or to hide image or to hide undesired elements in my sheet i imported also to make it on colors just like cad i wish there is answer for this

You arent listening. There is an answer for this. Layers isnt that answer.

Read up on Filters. Set one up for Interior walls, and set one up for Exterior walls. Turn them on, modify them, whatever. Way better than Layers.

Well, that's your problem. Revit isn't "just like cad".
Forget about layers and colors. It's not needed. In Revit, if you need to hide all of the wall, you do just that. Hide the walls. No need for layers. If you need to isolate a wall, you can use the isolate tool (the little pair of glasses at the bottom of the view).

It will be a little frustrating at first, but keep at it. You'll get the hang of it soon. Once it clicks, I promise you will never want to go back to autocad. I'm working on old project that just came back to life in ACA right now. I freakin' hate it! If I had time I'd redo it in Revit.

May I introduce you: Revit without layers - nice to meet you old fashioned layer fetishist.

No, Revit does not have layers. And believe us; layers are not good at all. They were invented at times when you probably even were not born yet. You may not agree right now, but Revit is great because it does not need to support such ancient wiggly ugly things.

So say goodbye to layers and say welcome to categories. In Revit you don't need to organize everything like you need to do in AutoCAD or other wiggly software. Everything is already organized in categories and subcategories. You can display or hide them. It is easy to hide furniture. Or hide those detail lines, or everything that you want or don't want. And you can have different views with different content and Revit always knows your intent (well, most of the time). This is the future; you are invited to leave the past.

But then, how to share data with that ancient wiggly software? At the time of export Revit data, there comes a layer definition file into the game. It defines for each Revit element category and subcategory the ACAD layer and style. To export means to lose all the intelligence of Revit. But you can do it and you can fulfill needs of authorities and clients, even different ones, because you can have different layer definition files.

I know at first this may look like a big change, but as soon as you got the trick, you would not want to go back.

And I also know, many people think that because it's from Autodesk, it must have layers. But fortunately that's not the case. Yes, Revit comes from the same house, but not from the same kitchen. The technology behind it is very young and completely different from those buggy crappy ugly wiggly ancient layered programs.

Just use the view properties “show/hide categories” or the VV shortcut. You can also right click and choose “Hide in viewElement or Category”

Ahmad,
Several things... We are all really helpful here and if you simply refrain from complaining and just ask a clear question from the start you will get great answers much faster. I am not surprised that many others haven't answered you already (as they would normally do)... your initial comment was a bit ...well I have nothing good to say about it, so I won't...

What I hear you asking is; You want to distinguish interior & exterior walls and turn them on & off at will: differently in different views" Correct?
If so you need to learn about Filters in Revit.

For instance, filters can see walls' "FUNCTION" and if the wall families are set correctly (Interior & Exterior) filters can be applied to Views to show, not show, override, change, etc. the walls seen in the filter(s) setup. It's actually quite simple & logical.

And for imported ACAD file you don't need layers to display or hide it. Simply just display or hide it as you like. Why would you want to do more work to make it more complicated?
A element in Revit knows that it is an element. A door for instance knows it's a door and that it belongs to the doors category. So just hide the door or the whole door category as you like. And don't mess with configurations and definitions like layers.

Layer Fetishist :-b ...perhaps the only fetish that is NOT k i n k y!!!