Edit > Duplicate Special

Creates one or more duplicates of the selection, optionally with transformations applied to each duplicate.

Edit > Duplicate Special >

Geometry Type

Select how you want the selected object(s) duplicated.

Copy: Make a copy of the geometry being duplicated.
Instance: Create an instance of the geometry being duplicated. When you create an instance, you do not create actual copies of the selected geometry. Instead, Maya redisplays the geometry being instanced.

Group under

Group objects under one of the following:

Parent: Groups the selected objects under their lowest common parent in the hierarchy.
World: Groups the selected objects under the world (at the top level of the hierarchy).
New Group: Create a new group node for the duplicates.

Smart Transform: Turn Smart Transform on so that when you duplicate and transform a single copy or instance of the object (without changing the selection), Maya applies the same transformations to all subsequent duplicates of the selected duplicate.
Translate, Rotate, Scale: Specify the offset values for X, Y, and Z. Maya applies these values to the copied geometry. You can position, scale, or rotate objects as Maya duplicates them.

NoteThe default for Translate and Rotate is 0.0000. The default for Scale is 1.0000. With the default values, Maya places the copy on top of the original geometry. You can specify offset values (positive or negative floating point) for translation, rotation, and scaling that are then applied to the copied geometry.
Number of Copies: Specify the number of copies to create. The range is from 1 to 1000.

TipAs a shortcut for duplicating with Smart Transform on, use Edit > Duplicate with Transform.
Duplicate Input Graph: Turn this option on to force the duplication of all upstream nodes leading up to the selected object. Upstream nodes are defined as all nodes with connections feeding into selected nodes.

For example, if A, B, and C are the upstream nodes connecting to D...

A > B > C > D

...and you select D and use the Duplicate Input Graph option, the resultant graph is as follows:

A1 > B1 > C1 > D1

(where A1, B1, C1, and D1 are duplicates of A, B, C, and D respectively).
Duplicate Input Connections: Turn this option on so that in addition to duplicating the selected node, the connections feeding into the selected node are also duplicated.

For example, if A, B, and C are connections feeding into C...

A > B > C

...and you select C and use the Duplicate Input Connections option, then the resultant graph is as follows:

A > B > C and

A > B > C1

(where C1 is a duplicate of C).
Instance Leaf Nodes: Duplicate entire node hierarchies except for the leaf nodes, which are instanced to the original hierarchy. The new menu item is an improvement over the existing instance menu item, in that all dynamic attributes on the non-leaf nodes are properly duplicated into the new hierarchy.
Assign Unique Name to Child Nodes: The child node is renamed when the hierarchy is duplicated.