The Battle of Nagashino (長篠の戦い, Nagashino no Tatakai) was a famous battle in Japanese history, fought in 1575 at Nagashino in Mikawa Province (present-day Nagashino, Shinshiro, Aichi Prefecture). The allied forces of Oda Nobunaga and Tokugawa Ieyasu (38,000) fought against Takeda Katsuyori's forces (15,000) and the allied forces won a crushing victory over the Takeda clan. As a result, Oda Nobunaga's unification of Japan was seen as certain.

In recent years, the battle has increasingly been referred to as the Battle of Nagashino and Shitaragahara (長篠・設楽原の戦い, Nagashino Shitaragahara no Tatakai). The battle started with an offensive over Nagashino Castle, followed by a battle at Shitaragahara, about 4 km to the west of the castle. Traditionally, the siege of Nagashino Castle by the Takeda forces and the decisive battle between the two main armies were regarded as a series of manoeuvres, and the battle was called the "Battle of Nagashino" after Nagashino, the name of a wide area in the region. However, if the emphasis is on the actual location of the battle (where the final battle took place), it is more appropriate to use "Battle of Shitara-gahara". Therefore, both place names are now listed together.

The battle is often cited as a turning point in Japanese warfare and as the first "modern" battle in Japan, as it was the battle in which Oda Nobunaga defeated the cavalry of the Takeda army with his powerful arquebusiers, using tanegashima.

The causes of victory for the allied forces used to be cited as the horse defensive fence (stockade) that prevented the advance of the Takeda cavalry, the three-stage shooting of 3,000 guns that fired in rapid succession in shifts of 1,000 guns each, and Katsuyori's reckless orders for a charge. However, recent research has led to the theory that the real cause of victory was something else. However, there is no doubt that matchlock guns played an active role, including in the sniping death of Yamagata Masakage, who was a famous general in the Takeda Army.

The trigger for the battle was the offensive between Tokugawa Ieyasu and Takeda Katsuyori over the North Mikawa region. The Takeda and Tokugawa clans had been at war with each other since the lifetime of Takeda Shingen. Nevertheless, the Takeda forces were overwhelmingly superior in terms of strength, and the Okudaira clan and other Okumikawa provincial leaders in the north-eastern part of the Mikawa region sought to prolong their lives by joining the Takeda side. On the other hand, Tokugawa Ieyasu had a powerful ally in Oda Nobunaga, but Nobunaga, who held the capital and was rapidly increasing his power, was by no means an equal ally. Ieyasu's position was that of a subcontractor who could not complain, although he called himself a cooperative company, and was used by Nobunaga as a good bulwark against the powerful Takeda forces. Takeda's forces had overrun Tokugawa territory on numerous occasions, but when Shingen fell ill during a campaign in Mikawa in May 1573, Takeda's forces retreated to Kai Province and worked to transfer power to Katsuyori while concealing Shingen's death. Ieyasu, sensing something unusual in the movements of the Takeda forces, shrewdly set out to rewind the situation. He maneuvered the kunishū (powerful families) of Okumikawa to regain the Northern Mikawa area from the Takeda clan.

Tokugawa forces sent Honda Tadakatsu and Sakakibara Yasumasa to capture the Nagashino Castle. Both of them managed to defeat the Takeda clan armies which guarded the castle and completed their mission to capture it. By recapturing Nagashino Castle, Ieyasu gained a strategic transport point, and made it his base in the region. In response, Takeda Katsuyori, who had finished his succession of power, led the main force of the Takeda army into the Okumikawa region. He then moved south along the Toyokawa River and ravaged the entire East Mikawa region, launching raids throughout the Tokugawa vassals' estates. Aside from that, Tadakatsu also captured many other castles in Tōtōmi Province from the Takeda clan.

In 1575, during the conflict between Oda-Tokugawa alliance against Takeda Katsuyori, when the latter invaded Enshū province, Tadakatsu and Sakakibara fought under the Tokugawa forces against Katsuyori, where they captured the Komyo castle in June.

In June 1575, Takeda Katsuyori invaded Mikawa Province. Katsuyori surrounded Nagashino Castle, which had only 500 defenders, with a large army of 15,000 men and launched an onslaught to make it a bridgehead for the Mikawa invasion. Tokugawa Ieyasu, in a difficult situation, decided that the Tokugawa army, which could mobilise only about 8,000 troops, could not stand against the Takeda army alone, and requested support from his ally Oda Nobunaga. At the time, Nobunaga had been engaged in battles with the Hongan-ji and Miyoshi clan for several years and was not normally in a position to go to Mikawa. However, he had just rested his soldiers after the battle had been brought to a halt when he attacked a castle built by the Hongan-ji and the Miyoshi clan offered to surrender. Nobunaga decided to throw the main Oda forces into Nagashino at once and left Gifu on 21 June. He led an Oda force of about 30,000 troops to Mikawa with his heir, Oda Nobutada, and joined Ieyasu at Okazaki on 22 June. Arriving at Shitaragahara on 26 June, he halted his march without going to the relief of Nagashino Castle and set up camp there. Nobunaga set up his main camp on Mount Gokurakuji, west of Shitaragahara, while Nobutada set up his camp on Mount Shinmido. Nobunaga set up camp on Shitaragahara because it was a depression. Taking advantage of the terrain, he positioned his 30,000-strong army so that it did not look like a large force from the Takeda side. Ieyasu set up camp on Mount Takamatsu in the front facing the Rengo River.