德意志聯邦共和國，簡稱西德或聯邦德國（德語：Bundesrepublik Deutschland，縮寫BRD）建立於1949年5月23日，其初期範圍包括二戰後由英國、美國和法國所占領的德國領土。在1990年兩德統一還都至柏林之前，西德的首都是設置於波恩。而除了德國西部的領土外，東德境內、德國原本的首都柏林市區西半部在當時也屬於西德領土。西柏林因為由東德領土包圍，是一個飛地。
在兩德統一之後，德意志民主共和國（東德）消失，由德意志聯邦共和國作為統一後的存續單位。
歷史
第二次世界大戰納粹德國戰敗，根據戰時波茨坦會議中英、美、法、蘇四國的秘約，决定在德國戰敗後將其一分為四分別由四個戰勝國占領，並且合組一個最高管理單位同盟管理議會（Allied Control Council，ACC）來治理德國事務。但由於理念上的差異，在戰後以美國為主的西方陣營與以蘇聯為主的共産陣營逐漸疏遠，1948年3月時，美、英、法三國在倫敦舉行會議，初步决議要將三國所分別管理的德國領土合併，組成一個德國西部的政權，針對這點蘇聯方面作出反製，首先是退出ACC，並進而宣佈着手設立一個東德政權的計劃。
但直接導致東西德分離的導火綫，則是發生在1948年6月20日，西方占領區境內的貨幣重整計劃。當時西方三國占領區內原本分別發行的貨幣整合為一，但卻排除蘇聯占領區，發行了所謂的西德馬剋，而蘇聯占領區也在短短三日後發行了東德馬剋，儼然象徵東西德正式分離。東西德分離後，東德方面曾在1948年中開始，對使用西德馬剋的西柏林地區進行封鎖，為期11個月，希望透過此舉達到完全控製整個柏林地區的目的，但卻在西方國傢持續以空運方式所進行的柏林空運之支援下沒有實現。在柏林封鎖解除（1949年5月12日）後沒多久的5月23日，西德（德意志聯邦共和國）宣佈正式成立。而東德方面也在同年的10月7日宣佈正式成立以德意志社會主義統一黨（縮寫：SED）一黨專政的社會主義共和政體。
西德於1955年5月8日加入北約，相對的，由蘇聯扶植、共黨主政的東德（德意志民主共和國）則加入了華沙條約組織，使得東西德間的交界成為兩大對壘陣營的最前綫，冷戰的焦點。
在1989年11月9日柏林墻倒塌後，東德領土於1990年10月3日正式並入西德，德意志聯邦共和國從此覆蓋德國全境，德國統一成一個國傢。1991年3月15日，四個占領國正式放棄對其的占領權。因此除了視為是一個分裂狀態下的獨立國傢之外，西德也可被視為是當代德國（德意志聯邦共和國）的一段歷史時期。
West Germany (German: Westdeutschland) is a common English name for the period of the Federal Republic of Germany (German: Bundesrepublik Deutschland, BRD) between the adoption of the new constitution in May 1949 to German reunification in October 1990, when the (East) German Democratic Republic was dissolved and the five states on its territory joined the Federal Republic of Germany, ending the more than 40-year division of Germany and Berlin. From the 1990 reunification onwards, the enlarged Federal Republic of Germany with sixteen states has been exclusively known as Germany in common usage.
The Federal Republic of Germany was organized from the initially 12 states formed in the three Western Zones or Allied Zones of occupation held by the United States, the United Kingdom, and France. Bonn was selected as its provisional capital city, rather than the enclave of West Berlin which had a special status, but practically was part of the Federal Republic. The fourth Allied occupation zone or East Zone (Ostzone) was held by the Soviet Union. The parts east of the Oder-Neisse were de facto annexed by the Soviet Union and Communist Poland, the remaining central part around Berlin became the communist German Democratic Republic, GDR (in German: Deutsche Demokratische Republik, DDR) with its de facto capital East Berlin. As a result, the remaining Western Germany had a territory about half the size of its previous democratic-capitalist antecessor, the interwar Weimar Republic.
At the onset of the Cold War, Europe and Germany were divided among the Western and Eastern blocs. Germany was de facto divided into two countries, plus two special territories, the Saarland and divided Berlin. The Federal Republic of Germany claimed an exclusive mandate for all of Germany, considering itself to be the democratically re-organized German Reich on the grounds that the GDR government was not democratically elected, but was installed by a foreign occupying power and thus not legitimate. The number of federal states changed in the 1950s, when three south western states merged to form a single Baden-Württemberg in 1952, and when the Saarland joined the Federal Republic of Germany in 1957. In addition to the official ten states, West Berlin was considered an unofficial de facto eleventh state. While legally not part of the Federal Republic of Germany, as it was under four-power occupation, West Berlin was represented directly or indirectly in federal institutions.
Relations with the Soviet bloc improved during the era of Ostpolitik in the 1970s, and the two German states recognized the existence of each other. De jure West Germany formally maintained the exclusive mandate: it recognized the GDR as a de facto government still within a single German nation that in turn is represented de jure by the West German state only, while East Germany recognized the existence of two German countries de jure, and the West as both de facto and de jure foreign country.
The foundation for the influential position held by Germany today was laid during the Wirtschaftswunder (economic miracle) of the 1950s, when West Germany rose from the massive destruction wrought by World War II to become the world's third largest economy. The first chancellor Konrad Adenauer, who remained in office until 1963, had worked for a full alignment with the West rather than neutrality. He not only secured a membership in NATO, but he was also a proponent of agreements that developed into the present-day European Union. When the G6/G8 was established in 1975, there was no question whether the Federal Republic of Germany would be a member as well.
When the system of state socialism collapsed in East Germany and the wider Central and Eastern Europe in 1989–1990, symbolized by the opening of the Berlin Wall, there was a rapid move towards German reunification. East Germany voted to dissolve itself and accede to the Federal Republic in 1990. Its postwar five states (Länder) were reconstituted, and along with reunited Berlin, which ended its special status and formed an additional Land, they formally joined the Federal Republic of Germany on 3 October 1990, raising the number of states from 10 to 16. The expanded Federal Republic of Germany, now exclusively known as simply Germany in the English language, retained its political culture, and it continues the memberships in international organizations, as well as its Western foreign policy alignment and affiliation to Western alliances like the European Union and NATO. The enlarged Federal Republic of Germany is the continuation of, and not a successor to, the (West German) Federal Republic of Germany with fewer states until 1990.
Western Germany (Westdeutschland or westliches Deutschland), where it is not a synonym for "West Germany", is mainly used as a geographic term referring vaguely to the Rhineland, a usage which dates back to before the Cold War. Citizens of the Federal Republic called their country Federal Republic, FR Germany or simply Germany. In the early years, the GDR termed the Federal Republic Westdeutschland, later the FRG (BRD). This abbreviation was strongly disliked by the West Germans as GDR jargon.