| Petru Rareș | |
| Succession: | Prince of Moldavia (1st reign) |
| Reign1: | 20 January 1527 – 18 September 1538 |
| Predecessor1: | Stephen IV of Moldavia |
| Successor1: | Stephen V of Moldavia |
| Succession2: | Prince of Moldavia (2nd reign) |
| Reign2: | 19 February 1541 – 3 September 1546 |
| Predecessor2: | Alexandru Cornea |
| Successor2: | Ilie II Rareș |
| Spouse: | Elena Ecaterina Rareș |
| House: | Bogdan-Mușat |
| House-Type: | Dynasty |
| Father: | Stephen the Great |
| Mother: | Maria Răreșoaia |
| Birth Date: | ca. 1483 |
| Birth Place: | Hârlău |
| Death Date: | 3 September 1546 |
| Death Place: | Suceava |
| Religion: | Orthodox |
Petru Rareș (in Romanian; Moldavian; Moldovan pronounced as /ˈpetru ˈrareʃ/), sometimes known as Petryła or Peter IV (Petru IV; – 3 September 1546), was twice voivode of Moldavia: 20 January 1527 to 18 September 1538 and 19 February 1541 to 3 September 1546. He was an illegitimate child born (probably at Hârlău) to Stephen the Great. His mother was Maria Răreșoaia of Hârlău, whose existence is not historically documented but who is said to have been the wife of a wealthy boyar fish-merchant nicknamed Rareș "rare-haired" (i.e., bald). Rareș thus was not Petru's actual name but a nickname of his mother's husband.
In his youth he was a fish merchant, but Prince Ștefăniță, grandson of Ștefan cel Mare, on his deathbed, recommended Petru as a suitable contender to the throne, thus acknowledging Petru's blood lineage from Ștefan cel Mare.
Petru exhibited many of his father's qualities: ambition, daring, bravery, piety, artistic taste. However, he was marked by inconstancy and a lack of political instincts.
In the Hungarian battles between Ferdinand Habsburg and John Zápolya, he initially sided with Ferdinand, but when the Ottomans awarded recognition to Zápolya, he switched allegiances. In exchange for the citadel of Bistrița, he entered Transylvania on Zápolya's side and crushed Ferdinand at Feldioara on 22 June 1529. Zápolya then gave him Ungurașul but in spite of the efforts made Rareș was unable to occupy Bistrița. Neither could he subdue Brașov, which he besieged again in October for several weeks. Thus he was far from realizing his plan of ruling Transylvania. He had to content himself with Ciceu and Cetatea de Baltă, ruled by his father, and with the bishopric of Vad.
He then shifted his attention to Poland and in 1530 occupied Pokuttya. The Polish general Jan Tarnowski soon reconquered it, but when Petru re-entered Pokuttya, he was defeated by Tarnowski through superior tactics at Obertyn on 22 August 1531.
Events forced him to return to Transylvania. Here, the Ottomans had dispatched an Italian adventurer, Lodovico Gritti, to restore order. Transylvanian voievod István Majláth and the country's nobles forced him to close himself in Mediaș. Since Petru had received orders from the sultan to free Gritti, he sent his trusted vassal Huru to do the job. However, instead of helping Gritti, Huru lured him out and delivered him to his enemies, who killed him on the spot (1534). Rareș then killed Gritti's sons, who had entered Moldavia. The Ottomans could not presently retaliate, being occupied in Persia, so Petru was free to continue his intrigues between Ferdinand and Zápolya. The Poles tried in vain to have him replaced in 1538, appealing to the sultan to punish him. Then the over-zealous Petru, deserted by his own boyars, his capital Iași ablaze, and faced with a Turkish-Tatar-Polish army headed by Suleiman the Magnificent, who was bringing Ștefan Lăcustă to the throne, had to flee to his Transylvanian fortress of Ciceu.