Hi Anis, although it is possible to import STL data using the plug-in Pilou mentions above, it's usually not a good idea to do that in MoI - MoI is designed to work with NURBS surfaces and solids and isn't designed to work with triangle mesh data (as is contained in STL format) during modeling time.

You should use a polygon mesh editing program to import and manipulate STL data, not MoI.

- Michael