Märzen or Märzenbier is a lager that originated in Bavaria and was traditionally brewed in March with moderate and balanced hopping levels, malt, and slightly higher alcohol content that would allow the beer to last while the brewing of new beer was forbidden from 24 April to 28 September. The beer was then allowed to lager in ice and straw-filled beer cellars until autumn. The original Märzen was described as "dark brown, full-bodied, and bitter". The beer was often kept in the cellar until late in the summer, and kegs were then served at the Oktoberfest. The modern Märzen is quite popular in America, imbibed at many Oktoberfest celebrations by the half liter or liter stein. Americans think of an “Oktoberfest” beer as a Märzen whereas in Germany, that beer would be a festbier. The Austrian style is generally lighter in color, body, and flavor. Other common names for Märzen include Märzenbier, Wiener Märzen, Festbier, and Oktoberfest bier.

Here are some key characteristics of the Märzen style beer:

• It is a lager that ranges in color from pale through amber to dark brown.
• It has a medium to full body.
• It has a sweeter and often less hoppy flavor than a Bavarian pale lager.
• It typically contains 5.1–6.0% alcohol by volume.
• It has a toasted bread or biscuit-like malt aroma and flavor.
• It is rich in malt with a balance of clean, hop bitterness, similar to the Vienna lager.
• It is "fest" strength, meaning it falls slightly higher in ABV than normal lagers of pilsner and helles with an ABV of 6% vs the normal 4.5-5%.

In summary, Märzen is a type of lager that originated in Bavaria and is traditionally brewed in March. It has a medium to full body and a sweeter and often less hoppy flavor than a Bavarian pale lager. It is rich in malt with a balance of clean, hop bitterness, similar to the Vienna lager, and is "fest" strength, meaning it falls slightly higher in ABV than normal lagers of pilsner and helles.