This article is about the Second Empire architectural style. For information about the government of France during the reign of Napoleon III of France, see Second French Empire. For information about the government of Germany from 1871 to 1918, sometimes called the "Second Reich," see German Empire.

Second Empire is an architectural style popular during the Victorian era, reaching its zenith 1865 and 1880, and so named for the “French” elements in vogue during the era of the Second French Empire. While a distinct style unto itself, some Second Empire styling cues, such as quoins, have an indirect relationship to the styles previously in vogue, Gothic Revival and Italianate eras. The canonical example of Second Empire style is the Opera Garnier in Paris.

In The United States, the Second Empire style usually combined a rectangular tower, or similar element, with a steep, but short, mansard roof; the roof being the most noteworthy link to the style’s French roots. This tower element could be of equal heighth of the top most floor, or could exceed the heighth of the rest of the structure by a story or two. The mansard roof crest was often topped with an iron trim, sometimes referred to as “cresting”. In some cases, lightning rods were integrated into the cresting design, making the feature useful beyond its decorative features. The exterior style could be expressed in either wood, brick or stone.

Floor plans for Second Empire residences could either be symmetrical, which placed the tower (or tower-like element) in the center or asymmetrical in nature in which the tower or tower-like element would be placed to one side.

The style also found its way in commercial structures, and was often used when designing state institutions. Prior to the construction of The Pentagon in the 1940s, the Second Empire-styled Ohio State Asylum for the Insane in Columbus, Ohio was documented as the largest building under one roof in America, proving the style's adaptability.

Second Empire was succeeded by the Queen Anne Style era, and its sub-styles, which enjoyed great popularity until the rise of the “Revival Era” in American architecture just before the end of the 19th century.