Browse through the beer section of any well-stocked store and you'll notice the word "imperial" showing up in front of many of your favorite beers: imperial stout, imperial pale ale, imperial pilsner and who knows what else. That word might actually mean something different than you think!
The term "imperial" was used in the 1800's for beer (usually stout) that was brewed in England but then shipped to Russia - specifically the imperial court of Russia! Brewers later started using the term more generally to indicate their top-of-the-line luxury beers.
With beers coming from American craft brewers these days, "imperial" is an indication that the beer is going to be big and bold regardless of the style. The hops and malts used during brewing are doubled or even tripled, and the resulting beer can pack quite an alcoholic punch ranging from 8% to 12% ABV.
These beers are definitely worth a try whenever you see them. If you like the basic style (stout, IPA, etc.), chances are that you'll enjoy the amped up imperialized version as well. They go well with rich, strongly flavored foods, and they make an excellent after-dinner sipping beer. Because they're so high in alcohol, one or two is usually our limit!
A few good ones to try are Left Hand's Imperial Stout, Dogfish Head's 90 Minute IPA (or 120 Minute IPA, if you can find it), and Rogue Ale's Imperial Pilsner.
What imperial beers have you had recently?
Related: Reserva, Riserva, Reserve: What Do They Mean For Wine
(Image: Flickr member Bernt Rostad licensed under Creative Commons)
Straw Mat from The ...

ipas are an absolute favorite. they're generally my go to beer. for all of their punch and severity they can also be remarkably subtle. maintaining the balance between overtness and overwhelming is tricky and i've definitely had some (read: many) which have gone overboard!
the simple clean finish on very hoppy ales is worth the effort to find for me.
some current favorites are green flash ipa (and double ipa,) huma lupa licsious, and dogfish 120 minute (though the 90 minute is also quite good.)
@nico_forgot: You just listed my favorite beers, with the exception of our house beer, Bell's Two-Hearted. Just tried the Green Flash Imperial IPA last night; fantastically hoppy and floral, gorgeously balanced. The 9.4% (!) is easy to miss, too. :)
The "I" in IPA stands for "India," not "Imperial." I have 100 pounds of empty brown bottles in the garage to prove it!
Rasputin Imperial Stout! :)
I'm going to have to agree with egosub2 on this one. IPA stands for India Pale Ale, not Imperial anything.
@eprewitt: bell's makes some fine beer. two hearted is a classic to me but i find their pale to be my favorite. third coast, best brown, and hop slam round out john's selection. i like but don't love his porters and stouts. i'm very glad that others have found the joys of huma!
I'm aware that the "i" in ipa is india. i just got to thinking about the imperial definition and how over the top some brewers take it. i appreciate your 100 pounds of brown bottles :) that's dedication to a fine art.
anyone in new england: ippswitch has a good ipa and so does opa! opa! out of easthampton (i think easthampton, maybe south though...sorry.) better than harpoon for my taste.
I love Old Rasputin, North Coast Brewing's Russian Imperial Stout. Definitely a beer to be sipped and savored.
To add to the confusion, Dogfish Head lists their 90 Minute and 120 Minutes as "Imperial India Pale Ales." IIPAs?! :)
Revisiting this, I think I was being an internet dickwad. Whoops.
That said, I think applying the "Imperial" label to ale is a little anachronistic and unnecessary. Wouldn't these fall into the existing category of "strong ale?"
Another vote in favor of North Coast Brewery's Old Rasputin. A fine brew.
I love Hop Czar from Bridgeport Brewing in Portland. It is an IIPA- Imperial India Pale Ale and it's delicious!
Green Flash is excellent. Also try Flower Power from Ithaca Brewing. Packed with hops.