I just received a copy of [IDL Primer](http://www.amazon.com/gp/redirect.html%3FASIN=0967127033%26tag=harmonicfunct-20%26lcode=xm2%26cID=2025%26ccmID=165953%26location=/o/ASIN/0967127033%253FSubscriptionId=0PZ7TM66EXQCXFVTMTR2) by Ronn Kling. (*Full disclousre: I received a free copy because Ronn used my [Periodic Table of IDL Operators](http://michaelgalloy.com/2006/11/01/periodic-table-of-idl-operators.html) on the back cover.*) It's a pocket sized “quick reference” that provides a quick introduction to the main functional areas of IDL: the IDL Environment (DE is covered, get Kling's [Navigating the Workbench](http://www.amazon.com/gp/redirect.html%3FASIN=0967127041%26tag=harmonicfunct-20%26lcode=xm2%26cID=2025%26ccmID=165953%26location=/o/ASIN/0967127041%253FSubscriptionId=0PZ7TM66EXQCXFVTMTR2) for coverage of the Workbench), syntax, array operations, program flow, 2D and 3D graphics, image processing, object graphics, file I/O, mapping, and animation. I have found it to be a quite handy reference, particularly the list of “Important Routines by Function” at the back (similar to the [Functional List of IDL Routines](http://idlastro.gsfc.nasa.gov/idl_html_help/Functional_List_of_IDL_Routines.html) in the online help).