Ninja Gaiden, later released in Europe as Shadow Warriors, is a 1988 side-scrolling beat-'em-up originally released by Tecmo as a coin-operated arcade video game. It was first released in North America, and Europe in 1988 and in Japan in 1989.

Ninja Gaiden is a series of video games featuring the ninja Ryu Hayabusa as its protagonist. The series is known as Ninja Ryukenden (忍者龍剣伝 Ninja Ryūkenden, lit. "Legend of the Ninja Dragon Sword") in Japan. The word "gaiden" in the North American Ninja Gaiden title means "side-story" in Japanese, even though the Ninja Gaiden series is not a spinoff of a previous series.

The arcade version of Ninja Gaiden is a side-scrolling beat-'em-up where the player controls a ninja hired to defeat an evil cult led by Bladedamus, a descendant of Nostradamus who seeks to fulfill his end of the world prophecies