Xenosaga Episode I: Der Wille zur Macht is a JRPG for the PlayStation 2 and the first title in the Xenosaga series, developed by Monolith Soft and published by Namco.

Der Wille zur Macht, German for "The Will to Power", is a reference to philosopher's Friedrich Nietzsche's concept of the main driving force in humans — namely, achievement, ambition, and the striving to reach the highest possible position in life. In other words, the power of will to succeed, make, change and create. It is also a reference to free will, a major theme of the game and series.

Xenosaga is set thousands of years into the future (sometime in the year 6000-7277 in the 61st century to 73th century), humanity exists only in deep space. Brutally opposed by a merciless hostile alien race called the Gnosis that are pushing humanity on the verge of extinction, humanity faces an uncertain destiny as it unlocks the secrets of the universe in search of the ultimate truth. Players take the role of scientist Shion Uzuki and her android KOS-MOS, as well as a ragtag cast of characters who become involved in the devastating conflict against the Gnosis.