Which ballet by Tchaikovsky is a classic Christmas tradition?

The ballet by Tchaikovsky that is a classic Christmas tradition is The Nutcracker.

The two-act ballet premiered at the Imperial Mariinsky Theatre in Saint Petersburg on December 18, 1892. Its Christmas Eve setting, toy characters, snow scene, and fantastical journey through the Kingdom of Sweets helped make it especially suited to holiday performances.

The story adapts Alexandre Dumas's 1844 version of E. T. A. Hoffmann's 1816 tale The Nutcracker and the Mouse King. Marius Petipa planned the choreography, with Lev Ivanov completing much of it, while Tchaikovsky wrote the score. The famous celesta gives the Sugar Plum Fairy's music its shimmering sound.

A common mix-up is confusing the complete ballet with The Nutcracker Suite. Tchaikovsky assembled the shorter concert suite before the full ballet premiered, and it became popular earlier. The staged ballet became a major annual tradition, particularly in North America from the late 1960s onward.