Potsdamer Platz (German: [ˈpɔtsdamɐ plats] ^ⓘ, Potsdam Square) is a public square and traffic intersection in the center of Berlin, Germany, lying about 1 km (1,100 yd) south of the Brandenburg Gate and the Reichstag (German Parliament Building), and close to the southeast corner of the Tiergarten park. It is named after the city of Potsdam, some 25 km (16 mi) to the south west, and marks the point where the old road from Potsdam passed through the city wall of Berlin at the Potsdam Gate. Initially, the open area near the city gate was used for military drills and parades. In the 19th into the 20th century, it developed from an intersection of suburban thoroughfares into the most bustling traffic intersection in Europe. The area was totally destroyed during World War II and then left desolate during the Cold War era when the Berlin Wall bisected it. Following German reunification in 1990, Potsdamer Platz underwent extensive redevelopment throughout the 1990s and early 2000s. Today, it is a bustling commercial and cultural hub featuring corporate offices, retail spaces, restaurants, cinemas, and hotels.

The history of Potsdamer Platz can be traced to 29 October 1685, when the Tolerance Edict of Potsdam was signed, whereby Frederick William, Elector of Brandenburg-Prussia from 1640 to 1688, allowed large numbers of religious refugees, including Jews from Austria and Huguenots expelled from France, to settle on his territory to repopulate it following the Thirty Years' War (1618–48). Several new districts were founded around the city's perimeter, just outside the old fortifications. The largest of these was Friedrichstadt, just south west of the historic core of Berlin, begun in 1688 and named after the new elector, Frederick William III, who became King Frederick I of Prussia. Its street layout followed the Baroque-style grid pattern much favoured at the time, and was based on two main axes: Friedrichstraße running north–south, and Leipziger Strasse running east–west. All the new suburbs were absorbed into Berlin around 1709–10. In 1721-3 a south-westwards expansion of Friedrichstadt was planned under the orders of King Frederick William I, and this was completed in 1732–4 by architect Philipp Gerlach (1679–1748). In this expansion, a new north–south axis emerged: Wilhelmstrasse.

In 1735–1737, after Friedrichstadt's expansion was complete, the Berlin Customs Wall was erected around the city's new perimeter. Potsdamer Platz would eventually develop around the gate at the west end of Leipziger Strasse, which turned south toward the hamlet of Schöneberg after leaving the city. This road, which had developed into part of a trading route running across Europe from Paris to St. Petersburg via Aachen, Berlin and Königsberg, became Elector Frederick William's route of choice to Potsdam, the location of his palace, in 1660. After Frederick II became king in 1740, the road was significantly improved, and became known as Potsdamer Straße; the gate became Potsdamer Tor (Potsdam Gate).

Just inside the gate was a large octagonal area, created at the time of Friedrichstadt's expansion in 1732-4 and bisected by Leipziger Strasse; this was one of several parade grounds for the thousands of soldiers garrisoned in Berlin at the height of the Kingdom of Prussia. Initially known as the Achteck (Octagon), on 15 September 1814 it was renamed Leipziger Platz after the site of Prussia's final decisive defeat of Napoleon Bonaparte at the Battle of Leipzig, which brought to an end the Wars of Liberation that had been going on since 1806. The gate itself was redesignated Leipziger Tor (Leipzig Gate) around the same time, but reverted to its old name a few years later.

Being outside Berlin, and therefore not subject to the same planning guidelines, Potsdamer Platz grew in a piecemeal and haphazard way, unlike Leipziger Platz, which had been planned and built all at once by Johann Philipp Gerlach. Prussian architect Friedrich David Gilly proposed a unified redesign of the two squares in 1797, but it was never built. In 1815, his pupil, Karl Friedrich Schinkel, proposed the area as the location for a National Memorial Cathedral, to be known as the Residenzkirche, but this was never built either, due to lack of funds. However, Schinkel did get to rebuild the gate in 1823–1824, replacing what was little more than a gap in the customs wall with a much grander affair consisting of two matching Doric-style stone gate-houses, like little temples, facing each other across Leipziger Strasse. The one on the north side served as the customs house and excise collection point, while its southern counterpart was a military guardhouse, set up to prevent desertions of Prussian soldiers, which had become a major problem. The new gate was dedicated on 23 August 1824. Schinkel's proposal to add a garden was not implemented, but in 1828 a plan by gardener and landscape architect Peter Joseph Lenné went ahead. He redesigned the Tiergarten, a large wooded park formerly the Royal Hunting Grounds, gave his name to Lennéstraße, a thoroughfare forming part of the southern boundary of the park very close to Potsdamer Platz, and transformed a muddy ditch to the south into one of Berlin's busiest waterways, the Landwehrkanal.

Meanwhile, country peasantry were generally not welcome in the city, and so the gates also served to restrict access. However, the country folk were permitted to set up trading posts of their own just outside the gates, and the Potsdam Gate especially. It was hoped that this would encourage development of all the country lanes into proper roads; in turn it was hoped that these would emulate Parisian boulevards—broad, straight and magnificent, but the main intention was to enable troops to be moved quickly. Thus Potsdamer Platz was off and running.

It was not called that until 8 July 1831, but the area outside the Potsdam Gate began to develop in the early 19th century as a district of quiet villas, for as Berlin became even more congested, many of its richer citizens moved outside the customs wall and built spacious new homes around the trading post, along the newly developing boulevards, and around the southern edge of the Tiergarten. The development was piecemeal, but in 1828 this area just to the west of Potsdamer Platz, sandwiched between the Tiergarten and the north bank of the future Landwehrkanal, received royal approval for a more purposeful metamorphosis into a residential colony of the affluent, gradually filling with palatial houses and villas. These became the homes of civil servants, officers, bankers, artists and politicians among others, and earned the area the nickname "Millionaires' Quarter" although its official designation was Friedrichvorstadt (Friedrich's Suburb), or the Tiergartenviertel (Tiergarten Quarter).

Many of the properties in the neighborhood were the work of architect Georg Friedrich Heinrich Hitzig (1811–81), a pupil of Schinkel who also built the original "English Embassy" in Leipziger Platz, where the vast Wertheim department store would stand, although Friedrichvorstadt's focal point and most notable building was the work of another architect—and another pupil of Schinkel. The Matthiaskirche (St. Matthew's Church), built in 1844–6, was an Italian Romanesque-style building in alternating bands of red and yellow brick, and designed by Friedrich August Stüler (1800–65). This church, one of fewer than half a dozen surviving pre-World War II buildings in the entire area, forms the centrepiece of today's Kulturforum (Cultural Forum).