Beer styles all fall into two broad types, determined by the time and temperature of the primary fermentation as well as where the yeast sits during fermentation: ales and lagers.

Ales

Ale is beer that is brewed using only top-fermenting yeasts, and is typically fermented at higher temperatures than lager beer.  At these temperatures, ale yeasts produce significant amounts of esters and other secondary flavors and aromas, oftentimes resembling those of apple, pear, pineapple, grass, hay, banana, plum or prune.
Typical ales have a sweeter, fuller body than lagers.

Pale ales are brewed using a pale barley malt, the classic example being the bitter of English pubs. Strengths vary from under 3% abv to over 20% in some rare barley wines. Hop levels also vary - ranging from barely noticeable to over 100 IBUs in some examples of India Pale Ale. India Pale Ale (IPA) was originally brewed to survive the journey from England to her colonies in Asia, well-hopped and high in gravity, but the term may be used today to indicate a session bitter or a super-premium pale ale.

A darker barley malt is used to produce brown ales, of which the English mild and Belgian oud bruin are examples. They tend to be lightly hopped, and fairly mildly flavored, often with a nutty taste.

Dark ales are brewed using dark-roasted barley malts. Porter was a London style that became extinct but has been revived in recent years, particularly in North America by companies such as Sierra Nevada. Porters range from brown to black in color; a version of porter using more highly roasted malt to give a black color was known as a "stout porter", or simply "stout". The English preferred sweet stout, typified by Mackeson's, a brew of around 3.75% to which milk sugars had been added. In Ireland dry stout became popular, exemplified by Guinness. Imperial Stout, or Imperial Russian Stout, is an even "bigger" style of 8-10%, originally exported as a winter warmer to the Russian court.

Irish red ale is a type of ale originating in Ireland. The slightly reddish color comes from the use of roasted barley, in addition to the malt. The beers are typically fairly low in alcohol (3.5% ABV typically), although stronger export versions are brewed. A red ale tastes less bitter or hoppy than an English ale, with a pronounced malty, caramel flavor.

Belgium produces a wide variety of specialty ales that elude easy classification. In addition to making a variety of blonde ale, all Trappist beer and virtually all Abbey beer are ales. Many Belgian ales are high in alcoholic content but light in body due to the addition of large amounts of sucrose, which provides an alcohol boost with an essentially neutral flavor.
Trappist beers are brewed under direct control of the monks themselves. Only seven Trappist monasteries brew beer, six in Belgium and one in the Netherlands. Abbey beer is brewed by commercial breweries using the name of a monastery, often one that no longer exists or sometimes, one that has licensed its name to a brewery.

Wheat beer is a beer that is brewed with a significant proportion of wheat. It is common for wheat beers to also contain malted barley. The addition of wheat lends wheat beers a light flavor and pale color. Hefeweizen is a German style of wheat beer in which the yeast is not filtered out.

Lagers

Lagers are the most commonly consumed type of beer in the world. Lagers are of Central European origin.  Lager yeast is a bottom-fermenting yeast, and typically begins fermentation at 7-12°C (45-55°F) (the "fermentation phase"), and then stored at 0-4°C (30-40°F) (the "lagering phase"). During the secondary stage, the lager clears and mellows. The cooler conditions also inhibit the natural production of esters and other byproducts, resulting in a "crisper" tasting beer.
Modern methods of producing lager were pioneered by Gabriel Sedlmayr the Younger, who perfected dark brown lagers at the Spaten Brewery in Bavaria, and Anton Dreher, who began brewing a lager, probably of amber-red color, in Vienna, Austria, in 1840–1841. With modern improved fermentation control, most lager breweries use only short periods of cold storage, typically 1–3 weeks.
Most of today's lager is based on the Pilsner style, pioneered in 1842 in the town of Pilsen (Plzeň), in an area of the Austrian monarchy now located in the Czech Republic. The modern Pilsner lager is light in color and high in carbonation, with a strong hop flavor and an alcohol content of 3–6% by volume. The Pilsner Urquell or Heineken brands of beer are typical examples of pilsner beer.

Pilsner or pilsener is a pale lager, developed in the 19th century in the Czech Republic .A modern Pilsner has a very light, clear color from pale, really pale up to a golden yellow, and a distinct hop aroma and flavor

American-style lager beer is a common variety of beer, a type of pale lager, traditionally made and consumed in North America, but also popular in much of the rest of the world. It derives ultimately from the Czech Pilsner, but is characterized by a much lighter color and body and the frequent use of rice or corn as adjuncts

Bock is a strong lager which has origins in the Hanseatic town Einbeck, Germany. The original Bocks were dark beers, brewed from high-colored malts. Modern Bocks can be dark, amber or pale in color.

Baltic porter

It has a higher alcohol content than ordinary porters. What was once a top-fermenting ("ale-style") beer, it is now mostly brewed as a lager-style bottom-fermenting beer in Slavic and Baltic breweries.

Hybrid beers

Hybrid or mixed style beers use modern techniques and materials instead of, or in addition to, traditional aspects of brewing. Although there is some variation among sources, mixed beers generally fall into the following categories: