Modern beer comes from five traditions: four European ones that cross-pollinated over the last 50 years, and an American one that took them apart and rebuilt them around hops. Ale vs lager lives in Beer Decoded; style-by-style detail lives in Beer Styles Decoded.
The 30-second cheat sheet
Tradition
Defining styles
Belgian
Tripel, Dubbel, Quad, Saison, Lambic, Witbier, Flemish Red
German
Helles, Märzen, Hefeweizen, Kölsch, Altbier, Berliner Weisse, Rauchbier
Czech
Czech Pilsner, Polotmavé, Tmavé
British
IPA (original), Porter, Mild, Bitter / ESB, Stout, Scotch Ale
American
West Coast IPA, NEIPA, American Pale Ale, modern Imperial Stout
Belgian
Belgium treats beer like wine, and centuries of monastic and farmhouse brewing made it the most stylistically diverse beer country on Earth.
Brussels and the Pajottenland is lambic country. The unfermented beer (wort) cools overnight in an open koelschip (coolship) and the local microflora ferment it. Nobody pitches yeast. Gueuze and Kriek start here.
Flanders, the Dutch-speaking north, ages Flemish Red and Oud Bruin in oak foeders: sour, but more controlled and wood-driven than lambic. Sour and Wild Beer Decoded covers both.
Wallonia, the French-speaking south, is Saison country. A saison ("season") was brewed in winter and stored for the saisonniers, migrant farmworkers who drank it during the summer harvest. The farmhouse original is rougher and funkier than American versions.
The through-line is yeast (think banana and clove), plus candi sugar for strong beer that still finishes dry. Witbier (wheat, coriander, orange peel) is Belgian too.
Trappist beer is brewed inside a monastery under monk supervision, with profits going to the order or to charity. The hexagonal "Authentic Trappist Product" seal is a legal certification. The Belgian five:
Abbey
Beers
Westvleteren
Blond, 8, 12, sold mostly at the abbey gate
Chimay
Red, Triple, Blue
Orval
One beer, dry-hopped, Brettanomyces in the bottle
Rochefort
6, 8, 10
Westmalle
Tripel (the beer that defined the style), Dubbel
Older lists include Achel, which lost the seal when its last monks left. La Trappe and Zundert (Netherlands) are certified too.
To understand Belgium, drink: Westmalle Tripel, Orval, a traditional Gueuze, then Saison Dupont.
German
The Reinheitsgebot ("purity law"), enacted in Bavaria in 1516, limited beer to barley, hops, and water. (Nobody knew yeast was a microorganism yet.) It's been amended and partially relaxed since, but for 500 years it pushed Germany toward precision over variety. Belgium experimented. Germany perfected.
Munich, pale and amber: Helles (pale and bready, around 4.7 to 5.4% ABV), Märzen (amber, brewed in March and lagered until autumn: the Oktoberfest beer), and today's paler Festbier.
Munich, dark and strong: Dunkel (the dark Munich lager), Bock, and Doppelbock (Doppelbock names traditionally end in -ator, after the Paulaner monks' Lenten "Salvator"). Also Hefeweizen.
Cologne: Kölsch, top-fermented but lagered cold, served in a slim 200ml Stange and nothing else (the tray ritual is in Glassware Decoded). Since the 1986 Kölsch Konvention, only Cologne-area breweries can use the name.
Düsseldorf: Altbier ("old beer," for the older top-fermenting method), dark amber and hoppier than most German beer. The two cities argue over which is correct. Both are.
Berlin: Berliner Weisse, a sour wheat beer around 3% ABV, traditionally cut with raspberry or woodruff syrup.
Bamberg: Rauchbier, from malt dried over beechwood fires. It tastes like smoked ham.
Dortmund: Dortmunder Export, a slightly stronger, drier pale lager built to travel.
To understand Germany, drink: Helles, Hefeweizen, Kölsch, Altbier, and Rauchbier. Every other German style sits between them.
Czech
Czechia drinks more beer per person than anywhere on Earth, and Plzeň gave its name to the Pilsner family, which covers most of the world's beer.
In 1842, Josef Groll at Plzeň's new municipal brewery combined pale malt (newly possible with indirect-heat malting), the town's soft water, and lager yeast from Bavaria. (Legend says a monk smuggled the yeast out; it was more likely just bought.) The result was the world's first golden lager, clear enough to show off in the glassware then coming into fashion, and within decades everyone had copied it badly. The original is slightly fuller than German Pils, with more Saaz hop and softer bitterness (Beer Styles Decoded has the side-by-side). Also look for Polotmavé (amber) and Tmavé (dark), both rare outside Czechia.
České Budějovice (Budweis) is the original Budweiser, not the lawn-mower beer. Budvar and Anheuser-Busch have fought over the name for more than a century. In much of Europe the American one is sold as "Bud."
In the hospoda (pub), the pour matters: hladinka is standard, with a creamy head about three fingers thick; šnyt is less beer and more head, for lunch; mlíko ("milk") is nearly all foam.
To understand Czechia, drink: unpasteurized tank Pilsner in a hospoda, under a thick hladinka head.
British
Britain's tradition is cask-conditioned ale: unfiltered and unpasteurized, finishing its fermentation in the pub cellar. It's hand-pulled at 52-55°F (11-13°C), and the soft carbonation shows flavor more clearly than any cold keg pour. CAMRA (the Campaign for Real Ale) was founded in 1971 to defend it. It's a session culture: 4% ABV and a long evening beat one big beer.
Burton-on-Trent water is loaded with gypsum, which made the hoppy pale ale Burton shipped to India sharper and drier. London's Bow brewery opened the India trade; Burton took it over in the 1820s and defined the IPA. Brewers still "Burtonise" water with gypsum.
London gave us Porter, probably named for the porters who drank it, and Stout, which began as a stronger "stout porter." Mild, the pub workhorse for most of the 20th century, nearly vanished and is creeping back.
Scotland is known for malt-forward, low-bitterness Scotch Ale (Wee Heavy).
Yorkshire ferments in the Yorkshire square, a two-story stone or slate vessel that gives its Bitter a slightly buttery edge. Bitter (around 3.5 to 4.5% ABV) is the everyday pint; Best Bitter is slightly stronger, and ESB runs around 5 to 5.8%.
Mild outsold bitter two pints to one in 1959, then slid fast as bitter and lager took over. Porter had it worse: British brewers stopped making it early in the Second World War. The revival started in San Francisco, where Anchor released a porter in 1972, and Timothy Taylor brought one back to British pubs in 1978.
To understand Britain, drink: a hand-pulled cask Bitter in a Yorkshire pub, a London Porter on a winter evening, and a Wee Heavy with something braised.
American
American craft is the youngest tradition (its modern era took off in 1980) and the least loyal. The question behind most of it: what if we used American hops in a [European style]?
California: Fritz Maytag rescued San Francisco's Anchor Brewing in 1965, and New Albion opened in Sonoma in 1976 as the first microbrewery of the modern era. Then Sierra Nevada Pale Ale (1980, Chico) rebuilt English pale ale around the new Cascade hop, grapefruit and pine instead of earth. Within a decade that became the bone-dry, bitter West Coast IPA. San Diego County sharpened it in the 1990s (Stone opened in 1996), and Vinnie Cilurzo brewed what's usually called the first double IPA at Blind Pig in Temecula in 1994.
Pacific Northwest: Washington's Yakima Valley grows roughly three-quarters of US hops; Cascade came out of the USDA breeding program at Oregon State University in 1972. Autumn means fresh-hop beer, made with undried hops and gone in about two weeks.
Vermont: NEIPA (hazy IPA) emerged roughly 2003 to 2010, chasing hop flavor over bitterness. The Alchemist's Heady Topper proved it, and within a decade NEIPA overtook West Coast IPA in many markets.
Chicago: Goose Island's Bourbon County Stout (first brewed 1992) largely proved the bourbon-barrel-aged imperial stout, a European style made American by spent whiskey barrels.
Elsewhere: Boulder got Colorado's first microbrewery in 1979, and the Great American Beer Festival started there in 1982 before moving to Denver. Asheville, North Carolina, a small city with a big brewery count, shared or won the Beer City USA poll in 2009 and 2010.
To understand American craft, drink: a Cascade-hopped Pale Ale, a West Coast IPA, a Vermont NEIPA, and a barrel-aged Imperial Stout. Four eras since 1980.
Trust the tradition over the label
A West Coast IPA is a British IPA with soft water instead of Burton's and Cascade instead of English hops. Style names drift (Saison especially). Tradition doesn't.
Drink beer where it was invented if you can, and fresh either way. For pairing logic, written for cocktails but it carries over, see Food Pairing: What to Drink With What.