In the course of the unification of the two German states, the political unity of Berlin was restored: Unification of Berlin (West) and Berlin (East) on October 3rd, 1990; Due to the unification of its previous special status, Berlin became a regular federal state of Germany (city-state). In the unification agreement of August 31, 1990, the contracting partners, the Federal Republic of Germany and the GDR, designated Berlin as the capital of Germany. Schwierzina and Momper (both SPD) jointly ran the city from October 3rd, 1990 to January 24th, 1991. The first free elections in Berlin as a whole (since 1946) on December 2nd, 1990 led to the formation of a CDU-SPD Senate at the constituent meeting of the new House of Representatives for Berlin as a whole on January 11, 1991 Diepgen; the constitution of Berlin (West) of September 1, 1950 (amended several times) became effective for all of Berlin on January 11, 1991. On October 1, 1991, the Senate moved its seat from Schöneberg Town Hall to the Red Town Hall. After the elections of October 22nd, 1995, in which the SPD suffered heavy losses and from which the PDS emerged as the strongest force in the eastern part of Berlin, the CDU-SPD coalition under Diepgen was continued; also after the elections on 10/10/1999. As a result of the Berlin banking scandal, the SPD officially terminated the grand coalition on June 10, 2001, and on June 16, 2001, K. Wowereit passed a “constructive vote of no confidence” against Diepgen elected as the new governing mayor; The SPD and Bündnis 90 / Die Grünen formed a transitional senate, tolerating the PDS. After the early election on October 21, 2001, from which the SPD emerged as the strongest force and the CDU lost 17% compared to 1999, an SPD-PDS Senate was formed under Wowereit (elected on January 17, 2002). The coalition of the SPD and the Left Party / PDS was continued after the election on September 17, 2006 under Wowereit (re-election in the second ballot on November 23). In the election on September 18, 2011, the SPD was able to assert itself as the strongest force for the third time in a row, despite slight losses. The Pirate Party achieved a surprise success with 8.9%, which was the first time that it entered a state parliament. Under leadership Wowereits (Re-election in the first ballot on November 24th) the SPD formed a coalition with the CDU. On December 11, 2014, Wowereit resigned as Governing Mayor. The House of Representatives elected M. Müller (SPD) as his successor. Under his leadership, the SPD recorded its worst election result in Berlin after the Second World War in the elections for the House of Representatives on September 18, 2016 with only 21.6% of the votes, but remained the strongest political force ahead of the CDU, which with 17.6% in Berlin also fell to an all-time low. The AfD, which took part for the first time, immediately received 14.2% of the votes. The SPD, the Left and the Greens agreed to form a coalition, the first national red-red-green state government under the leadership of the SPD. On December 8th, 2016 M. Müller re-elected Governing Mayor.
In a terrorist attack on a Berlin Christmas market on Breitscheidplatz by the Kaiser Wilhelm Memorial Church on December 19, 2016, at least twelve people were killed and over 50 were injured, some seriously. A truck drove into the crowd at the Christmas market.
On June 20, 1991, the German Bundestag decided to move the seat of parliament and government from Bonn to Berlin after a transitional period (later specified for the period between 1998 and 2000); An agreement between the federal government and the states of Berlin and Brandenburg was signed on August 25, 1992 to expand Berlin as the capital (capital city contract); It regulates the cooperation between the Federal Government and the Berlin Senate in the urban development of Berlin (including the parliamentary and government district) and cooperation with Brandenburg. The relocation of the Bundestag and federal government as well as ministries and federal institutions to the federal capital Berlin took place in accordance with the Berlin / Bonn Act from April 26, 1994. On September 27, 1996, the Federal Council also decided to move its seat to Berlin (it took place in 2000). The Federal President has had his first official residence in Bellevue Palace since January 1994. The German Bundestag and Federal Government have had their seat in Berlin since September 1, 1999.
A unification of the states of Berlin and Brandenburg in 1999 or 2002 (founding state treaty of April 27, 1995) was rejected by a majority in a referendum on May 5, 1996.