The Battle of Rymnik or Rimnik, also Battle of Mărtinești (Turkish: Boze Savaşı [Battle of the Boze]; Russian: Рымникское сражение [Battle of the Rymnik]; German: Schlacht am Rimnik), on September 22 [O.S. September 11] 1789, took place in Wallachia, at the Râmnicul Sărat River, known as the Rymnik, near Râmnicu Sărat or Rymnik (now in Romania) during the Russo-Turkish War of 1787–1792 and the Austro-Turkish War of 1788–1791. The Russian general Alexander Suvorov, acting together with the Habsburg general Prince Josias of Coburg, attacked the main Ottoman army under Grand Vizier Cenaze Hasan Pasha, which was much larger.

The result was a crushing Russo-Austrian victory. Although this battle was fought in accordance with Suvorov's intentions, the Austrians made up the bulk of the victorious allied troops. According to Suvorov's plan, while the Russians executed their deep, complex flanking attack on the Ottoman left wing across broken ground, the Austrians bore the brunt of the Ottoman attack. Their force was almost surrounded on the left, but they held on, and with the help of Suvorov's reinforcements, they managed to throw the enemy back. Ultimately, the general attack on the main Ottoman foothold broke the army's spirit, and its defeat was completed in the subsequent pursuit. Thus the Ottomans were decisively defeated piecemeal. The battle is regarded as one of the most noteworthy feats of military history and one of Suvorov's greatest achievements. For this battle, he received the addition Rymniksky to his family name and the title of count.

After Suvorov's retreat from Switzerland, the Prince of Coburg wrote to Suvorov that he appreciated the events he had gone through with him in the Turkish war and regretted that the Russian general had not been able to achieve the upper hand.

In September 1789, the Ottoman vizier Cenaze Hasan Pasha, vowing revenge for their forces' defeat at Focșani, raised an army of up to 100,000 men, with 40,000 janissaries and 40,000 cavalry including sipahi and deli, to defeat the combined Austro-Russian armies under generals Alexander Suvorov and Prince Josias of Coburg, the future heroes of the French Revolutionary Wars. Sending his troops into a grueling night march from Brailov (now Brăila), the Pasha attacked the 18,000-strong Austrian detachment. Taking into account Josias's numbers and the Austrian underperformance in the war, specifically after the so-called "Battle of Karánsebes", the Battle of Slatina, and the Battle of Mehadia, the Pasha was convinced that he could defeat this force easily; much of the reason for the Austrian setbacks was their tactic of a thin stretched front. However, the Austrian commander repulsed the Turks after a fierce skirmish on the 19th and appealed for help to Suvorov, who was with a division south of Bârlad. Following a hard fought combat, Coburg realised that he was in danger if the main forces attacked him. Once Suvorov heard of the Ottoman advance, he succinctly replied "Coming, Suvorov." and his 7,000-strong Russian force quickly marched to their aid on the night of 19 September and covering about 60 miles (97 km) in two and a half days, having arrived on the eve of battle on 21 September and joining forces with Prince's troops. Of Suvorov's generals under him, only Major-General Poznyakov (front line), and two brigadiers. Major-General Karaczay under Coburg, the hero of that skirmish, watched the road to Râmnicu Sărat and Buzău; he would fight bravely at the Rymnik as well.

Turkish troops were stationed in the basin of the Rymna (now known as the Râmna) and Rymnik Rivers in several fortified camps 6–7 kilometres (3.7–4.3 mi) apart. The Austrian commander proposed a defensive plan, arguing that the Turks had an overwhelming superiority in strength and occupied strongly fortified positions. Suvorov insisted on an immediate offensive. His plan was to defeat the enemy piecemeal. The battle order of the Russian and Austrian troops built before dawn on 22 September was 2 lines of infantry squares, behind which the cavalry was placed. The battle began and took place according to Suvorov's plan.

Suvorov, recognizing the dangers of a direct approach due to the steep banks of the Rymna and the visibility to the enemy, opted for a lower crossing point. While the Russians replenished their energy with food from the Austrians, Suvorov shared his strategy with Coburg. Despite Coburg's concerns about the numerical inferiority of the allies (almost 4 to 1), Suvorov reassured him, emphasizing that a larger enemy would create chaos and make it easier for them to advance; "That's all right," he is supposed to have said. "The greater the enemy the more they will fall over one another, and the easier it will be for us to cut through. In any case, they're not numerous enough to darken the sun for us", continued the Russian commander. Suvorov, aware of the risks but focused on boosting morale, took charge of the right flank. He knew that Turkish forces were positioned in Tyrgo Kukuli wood on the right side of the crossing and planned to neutralize them before advancing towards the main Turkish position at Kryngior Melor wood and the River Rymnik. The Austrians were to hold their position in the center while the Russians executed this detour. Suvorov's troops faced a tougher challenge, contingent upon the Austrians maintaining their stance.

That evening, as the sun set, infantry marched out in columns, led by cavalry. "The night was pleasant, the sky speckled with stars." They moved silently. Major Voyevodsky, a military engineer, discovered a crossing point on the Rymna River. Advance troops cleared the steep banks for easy passage of guns, wagons, and other equipment. Once across, they formed 6 squares with cavalry behind and advanced towards the Ottoman camp at Tyrgo Kukuli, 4 miles (6.4 km) to the south. Turkish cannons fired as Suvorov's guns retaliated.

On the far left, the Russian square was almost at a deep gully when 12,000 troops surged out to break it up. Lieutenant-Colonel Khastatov's grenadiers struggled to hold their ground. The square's edges were breached in multiple places, and the reserve soldiers inside fought desperately to maintain formation. They grew tired of pushing Turks off their bayonets. The nearby square fired a barrage of bullets at the mass attacking them. After half an hour, the Turks retreated, chased by Austrian hussars alongside the Russians. Sergeant Major Kanatov and a group of Ryazan Carabiniers captured a standard from a group of 40 Turks. Suvorov's corps shifted left to assist Coburg, who was under attack by 20,000 men led by Hadji Soytar after crossing the river later than the Russians.