The 2013 US Brewers Association Beer Style Guidelines have just been released. While I don't believe a beer must match its style exactly down to the very last ingredient, SRM value, and IBU value (they really are just 'guidelines' after all) I've always found this style guide a useful tool in designing a beer recipe. I'm a firm believer in knowing what the rules are before before you start breaking them.
My only gripe is that while it contains guidelines for such obscure beers type as Grätzer or Bamberg-Style Märzen Rauchbier, there's no style guidelines for New Zealand Draught. I guess they don't drink a lot Speights in the US craft/home-brew scene.
The 2013 beer style guidelines are available for download from BrewersAssociation.org here.
