From BlenderWiki

Duplicate

Description

This will create a visually identical copy of the selected object(s). The copy is created at the same position as the original object and you are automatically placed in Grab mode. Reference (Duplicate Example) for the discussions below.

This copy is a new object, which “shares” some datablocks with the original object (by default, all the Materials, Textures, and Ipos), but which has copied others, like the mesh for example. This is why this form of duplication is sometimes called “shallow link”, because all datablocks aren’t shared, some of them are “hard copied”!

Note that you can choose which types of datablock will be linked or copied when duplicating: in the User Preferences window (should be the one at the top of your screen), click on the Edit Methods “tab”, and in the Duplicate with object: buttons group, activate those corresponding to the types of datablocks you want to really copy - the others will just be linked.

Examples

The cone labeled “C” is a Duplicate of cone “A”. Here are some properties to notice:

• The vertex at “P1” has been moved but the same vertex on cone “A” is unchanged. This means the mesh data are copies, not links.
• Cone “C”’s color is red because cone “A”’s color is red. This means the material properties are linked not copied.
• If you rotate cone “C”, cone “A” remains unchanged. This means the transform properties (i.e. Object datablocks) are copies, not links.

See above if you want separate copies of the datablocks normally linked.

Linked Duplicates

Description

You also have the choice of creating a Linked Duplicate rather than a Duplicate; this is called a deep link. This will create a new object with all of its data linked to the original object. If you modify one of the linked objects in Edit mode, all linked copies are modified. Transform properties (object datablocks) still remain copies, not links, so you still can rotate, scale, and move freely without affecting the other copy. Reference (Duplicate Example) for the discussions below.

Examples

The cone labeled “D” is a Linked Duplicate of cone “B” using AltD. Here are some properties to notice:

• The vertex at “P2” has moved and the same vertex on cone “B” has moved as well. This means the mesh data are links, not copies.
• Cone “D”’s color is green because cone “B”’s color is green. This means the material properties are also linked and not copied.
• If you rotate cone “D” cone “B” remains unchanged. This means the transform properties are copies, not links.

A common table has a top and four legs. Model one leg, and then make linked duplicates three times for each of the remaining legs. If you later make a change to the mesh, all the legs will still match. Linked duplicates also apply to a set of drinking glasses, wheels on a car… anywhere there is repetition or symmetry.

Procedural Duplication

There are currently four ways in Blender to procedurally duplicate objects. These options are located in the Object context (F7), panel Anim settings.

DupliVerts

This creates an instance of all children of this object on each vertex (for mesh objects only).

DupliFaces

This creates an instance of all children of this object on each face (for mesh objects only).

DupliGroup

This creates an instance of the group with the transformation of the object. Group duplicators can be animated using actions, or can get a Proxy.

DupliFrames

For animated objects, this creates an instance on every frame. As you’ll see on this topic’s subpage, this is also a very powerful technique for arranging objects and for modeling them.

Linked Library Duplication

Linked Libraries are also a form of duplication.

Hints

If you want transform properties (i.e. object datablocks) to be “linked”, see the page on parenting.