Libraries Panel
The Libraries command opens the Libraries panel to manage libraries of materials, textures, and environments.
Rendering content can be saved to files to create external libraries that can be shared between models. Content can also be dragged between Rhino sessions and into a folder.
Color swatches can be dragged and dropped in the same way.
The Libraries panel displays a view into the content folders you have set up. Use this to drag and drop content into the model or to store document content to a location outside the model.
Materials are simply files on your hard drive. Library folders are simply Windows folders. You can copy and paste and move folders around just as you would any Windows file or folder.
Use the address bar at the top of the Libraries tab to navigate to any folder on your computer.
To quickly navigate back to the Default Library locations use the wrench icon at the upper right. 
Organizing Libraries
Libraries are simply files. You can copy and paste and move around folders. Use Windows Explorer to edit the folders and documents. To edit which folders are the default in the Libraries Tab, use the Library Settings .
Materials Library
Materials in libraries are files on the hard drive. Once assigned to the model, the material is then stored and saved in the model. Any changes to the assigned material will not change the original material on the hard drive.
Drag and drop materials to assign materials to the model. Materials can be assigned to:
Layer Assignment
Drag a material directly onto the layer name in the Layers Panel. This is the recommended method as by default any object on the layer will adopt the material assignment. Later changes to the material can be quite quick by simply dropping another material on the layer.
Object Assignment
Drag a material directly onto an object in any viewport. This will override the By Layer material to a By Object assignment.
Block Assignment
Drag onto a block and any By Parent objects in the block will adopt that material. Any object within the block that has a By Parent material source will pick up the blocks material.
Plant Library
In the default library folder is a Plants folder. Go here to place plants in the model. Once placed in the model, the plant is then stored and saved in the model. Any changes to the assigned plant will not change the original plant on the hard drive. Drag and drop plants into a viewport to place plants into the model. For more information see the Plants Help topic.
Environment Library
Environments can be saved in the library. This lets Environment settings to be passed from one model to another. For more details, go to Environments.
Library Settings
Use 
Libraries Options to change the library defaults shown under the menu.
Where can I find this command?
There are three places to find the Libraries Options command.
- Libraries Tab > in the upper right of the Libraries panel > Settings…
- Menus > Tools pulldown > Options > Libraries.
- Menus > Panels > Libraries.
Show render content
Use this to show or hide the default render content location.
Use default library location (My Documents)
By default, the content libraries are a subfolder of the My Documents folder.
Custom
Sets a custom library location. Changes the default location of content libraries for this computer.
Browse button
Open file browser to specify file.
Show Documents folder
In the Libraries panel, the designated Documents folder will display in the menu.
Show custom folders
In the Libraries panel, designated custom folders will display in the menu.