The flag of Germany was adopted in its present form in 1919. It was readopted with the new constitution of 1949. It is a tricolour, made of three equal horizontal bands coloured black (top), red, and gold.

Origins
There are two main theories about the exact origins of these colours. The first claims they go back to the uniforms (mainly black with red facings and gold buttons) of the Lützow Free Corps, comprised mostly of university students, that formed during the end of the struggle against the Napoleonic occupation of much of Germany. The other holds that they are derived from the black eagle on gold on the Imperial coat of arms of the Holy Roman Empire. Under this latter theory, the explanation of the red could either be simply that the eagle also had a red beak and red talons, or alternatively that it was the colour of revolution and liberty being added to the historical imperial colours. The explanation of the flag's colours is fraught with much debate, and there was a political desire for a distinctive tricolor to be adopted as the national flag to counter that of defeated France. These motives could have led to a tenous historical origin becoming cleverly elaborated in order for the flag to be widely accepted. Whatever the true explanation, these colours soon came to be regarded as the national colours of Germany during the period of the German Confederation in the first half of the 19th century. The revolutionary year of 1848 saw a nationalistic and liberal movement try to transform the loosely-knit Confederation into a more unified and free state. When the Frankfurt Parliament convened on March 9, 1848, they declared them as official federal colours and adopted the black-red-gold (schwarz-rot-gold) flag.

German Confederation (only 1848)

However, Prussia, the most influential German state, resisted this movement, and worked to establish a unified Germany more favourable to Prussia's interests. An important step in this direction was the founding of the North German Confederation in 1867, which on June 25 of that year adopted a flag that blended the Prussian colours (black and white) and the colours of the Hanseatic League (red and white) into a new black-white-red (schwarz-weiß-rot) horizontal tricolour. This flag would also be the national flag for the subsequent German Empire from 1871 to 1918, which finally replaced the German Confederation.

North German Confederation (1867-1871), German Empire (1871-1918)

Following Germany's defeat in World War I this Imperial flag fell into disuse and the new Weimar Republic officially reinstated the black-red-gold sequence on August 11, 1919.

Weimar Republic (1919-1933)

Throughout the days of the Weimar Republic there was a debate on which flag to use, causing strong controversy, with monarchists in favour of re-adopting the black-white-red flag. In 1926 the old black-white-red flag was allowed to use in the foreign service of Germany again.

Weimar Republic (1926-1935) (co-official with previous flag used in diplomatic representation)

When the Nazis came to power in 1933 the black-red-gold flag was entirely removed and replaced with the black-white-red, though they would eventually, on September 15, 1935, replace virtually all German governmental flags with designs based on the swastika flag that had been their party flag. It featured the same colours as the Imperial flag, but it was arranged as a red flag with a white disk in the centre containing a black swastika. The old black-white-red flag was then banned by the Nazis as "reactionary".

Third Reich 1935-1945 (jointly with previous flag 1933-35)

After the defeat of Germany in World War II, Germany was occupied by the Allies. The occupation government banished the existing national flags, and issued an order designating the international signal pennant representing the letter "C" (minus a triangular cutout) as the ship flag of Germany. "C" stands for Capitulation.

The black-red-gold flag was once again adopted as the federal flag for the Federal Republic of Germany (West Germany) on May 9, 1949. The German Democratic Republic (East Germany) had initially used the same flag, but on October 1, 1959 it introduced a communist emblem to the centre of the flag: a hammer (symbolizing the workers), and a pair of compasses (symbolizing the intellectuals) inside ears of grain (symbolizing the farmers). This remained almost until the territory of the the former GDR was reunified with the Federal Republic of Germany in 1990 (the GDR formally removed the emblem shortly before reunification). The flag of the GDR was banned, and any use of it considered a criminal offense, in West Germany during much of the Cold War.

(Flag of the German Democratic Republic) GDR (1959-1990)