The current version of this post will be maintained at http://genweblog.blogspot.com/2006/11/using-batch-numbers-and-igi.html
What are Batch Numbers and how are they useful?
You will find Batch numbers in IGI (International Genealogical Index) records on the FamilyHistory.org website, or researching at your local Family History Center. Here is a bit of expanation from Rhonda McClure, from an old Family Tree Finders post. Start with the fiche
"IGI Batch Number Index" ...still available at your local Family History Center .... is a valuable tool when trying to understand the origins of any entries in the IGI. This is also the fiche you [will] use for converting the batch number manually. The fiche is useful when you have printed out information from FamilySearch.org and have many of those to check. If you are doing your research at the Family History Center, then it is easier to just print out the entries (use the F2 function to save a group of them to print to a single page) as that will give you the film numbers.- Rhonda R. McClure
You can then take the film numbers and search either online or in the FHC and see exactly what the film is about. For a detailed chart about this you may want to see an article I wrote on this over on Genealogy.com. It was in answer to a similar question, but offers a chart of the more common batch numbers and what type of resource they refer to. You can see that article at http://www.genealogy.com/genealogy/heard070199.html.
New Zealand Society of Genealogists has another method: http://www.nzsghamilton.co.nz/igi.htm
Making Optimum Use of the IGI, by Helen Schatvet Ullmann, CG, FASG: http://www.livgenmi.com/fhcigi.htm
Although a bit out of date, the GenUKI site has a good page on finding and using batch numbers: http://www.genuki.org.uk/big/FindingBatchNos.html
See Hugh Wallis's wonderful site, IGI Batch Numbers - British Isles and North America: http://freepages.genealogy.rootsweb.com/~hughwallis/IGIBatchNumbers.htm
German IGI Batch Number Index: http://www.igi-index.de/?seite=batch8&lang=uk
Since the site is in German, it's a bit difficult to use until you are used to it. Click on the letter of the alphabet that begins your town of interest, and scroll down to your place. Or, substitute your place of interest in the URL (for the XXXs): http://www.igi-index.de/?seite=batch8&lang=uk&sort=ort&id=XXX
IGI Batch Number Instructions: http://www.rawlins.cnchost.com/igi.html
IGI Batch-Nummern: http://freepages.genealogy.rootsweb.com/~carlbecker/igi_batch.htm (Hessen / Hessen-Nassau, Baden, Württemberg, Bayern (hauptsächlich Pfalz), Rheinland, Westfalen, Lippe / Schaumburg-Lippe, Preußen (sofern nicht bereits aufgeführt), Sonstige)
Microfilming of French Records: http://www.geneaguide.com/anglais/microfilmfrenchrecord.htm
Even if you're on the right track, you'll get run over if you just sit there. - Will Rogers