Mieszko I of Poland in the context of "Poland during the Piast dynasty"

The House of Piast was the first historical ruling dynasty of Poland. The first documented Polish monarch was Duke Mieszko I (c. 960–992). The Piasts' royal rule in Poland ended in 1370 with the death of King Casimir III the Great.

Branches of the Piast dynasty continued to rule in the Duchy of Masovia (until 1526) and in the Duchies of Silesia until the last male Silesian Piast died in 1675. The Piasts intermarried with several noble lines of Europe, and possessed numerous titles, some within the Holy Roman Empire. The Jagiellonian kings ruling after the death of Casimir IV of Poland were also descended in the female line from Casimir III's daughter.

The history of Poland spans over a thousand years, from medieval tribes, Christianization and monarchy; through Poland's Golden Age, expansionism and becoming one of the largest European powers; to its collapse and partitions, two world wars, communism, and the restoration of democracy.

The roots of Polish history can be traced to ancient times, when the territory of present-day Poland was inhabited by diverse ethnic groups, including Celts, Scythians, Sarmatians, Slavs, Balts and Germanic peoples. However, it was the West Slavic Lechites, the closest ancestors of ethnic Poles, who established permanent settlements during the Early Middle Ages. The Lechitic Western Polans, a tribe whose name denotes "people living in open fields", dominated the region and gave Poland - which lies in the North-Central European Plain - its name. The first ruling dynasty, the Piasts, emerged in the 10th century AD. Duke Mieszko I, regarded as the creator of Polish statehood, adopted Western Christianity in 966 CE. Mieszko's dominion was formally reconstituted as a medieval kingdom in 1025 by his son Bolesław I the Brave, known for his military expansions. The most successful and the last Piast monarch, Casimir III the Great, presided over a period of economic prosperity and territorial aggrandizement before his death in 1370 without male heirs.

The period of rule by the Piast dynasty between the 10th and 14th centuries is the first major stage of the history of the Polish state. The dynasty was founded by a series of dukes listed by the chronicler Gall Anonymous in the early 12th century: Siemowit, Lestek and Siemomysł. It was Mieszko I, the son of Siemomysł, who is considered the founder of the Polish state. Mieszko converted to Christianity of the Western Latin Church in an event known as the Baptism of Poland in 966. His acceptance of Christianity marked the formal beginning of Polish statehood, which was recognized by the Papacy and other Christian states of Europe. The Papal incipit titled Dagome iudex, first defined Poland's geographical boundaries and affirmed that Mieszko was under the protection of the Apostolic See. Mieszko also completed a unification of the Lechitic tribal lands that was fundamental to the existence of the new country of Poland. The ruling house then remained in power in the Polish lands until 1370.

Following the emergence of the Polish state, a series of rulers converted the population to Christianity, created a kingdom of Poland in 1025 and integrated Poland into the prevailing culture of Europe. Mieszko's son Bolesław I the Brave established a Roman Catholic Archdiocese in Gniezno, pursued territorial conquests and was officially crowned in 1025 as the first king of Poland. The first Piast monarchy collapsed with the death of Mieszko II Lambert in 1034, followed by its restoration under Casimir I in 1042. In the process, the royal dignity for Polish rulers was forfeited, and the state reverted to the status of a duchy. Duke Casimir's son Bolesław II the Bold revived the military assertiveness of Bolesław I, but became fatally involved in a conflict with Bishop Stanislaus of Szczepanów and was expelled from the country.

Bolesław I the Brave (c. 967 – 17 June 1025), less often known as Bolesław the Great, was Duke of Poland from 992 to 1025 and the first King of Poland in 1025. He was also Duke of Bohemia between 1003 and 1004 as Boleslaus IV. A member of the Piast dynasty, Bolesław was a capable monarch and a strong mediator in Central European affairs. He continued to proselytise Western Christianity among his subjects and raised Poland to the rank of a kingdom, thus becoming the first Polish ruler to hold the title of rex, Latin for king.

The son of Mieszko I of Poland by his first wife Dobrawa of Bohemia, Bolesław ruled Lesser Poland already during the final years of Mieszko's reign. When the country became divided in 992, he banished his father's widow, Oda of Haldensleben, purged his half-brothers along with their adherents and successfully reunified Poland by 995. As a devout Christian, Bolesław supported the missionary endeavours of Adalbert of Prague and Bruno of Querfurt. The martyrdom of Adalbert in 997 and Bolesław's successful attempt to ransom the bishop's remains, paying for their weight in gold, consolidated Poland's autonomy from the Holy Roman Empire.

The Christianization of Poland (Polish: chrystianizacja Polski [xrɘs.tja.ɲiˈza.t͡sja ˈpɔl.ski]) refers to the introduction and subsequent spread of Christianity in Poland. The impetus to the process was the Baptism of Poland (Polish: chrzest Polski [ˈxʂɛst ˈpɔl.ski]), the personal baptism of Mieszko I, the first ruler of the future Polish state, and much of his court. The ceremony took place on Holy Saturday, 14 April 966 (under the Julian pre-Gregorian calendar, equivalent to 19 April 966 Gregorian), although the exact location is disputed by historians, with the cities of Poznań and Gniezno being the most likely sites. Mieszko's wife, Dobrawa of Bohemia, is often seen as a major influence on Mieszko's decision to accept Christianity.

While the spread of Christianity in Poland took centuries to finish, the process was ultimately successful, as within several decades Poland joined the rank of established Christian polities recognised by the papacy and the Holy Roman Empire. According to much histioriography, the baptism of Poland marks the beginning of Polish statehood. Nevertheless, the Christianization was a long and arduous process, as most of the Polish population remained pagan until the pagan reaction during the 1030s.