From the liner notes

Alien
A space ship answers what they believe to be a distress call, and unwittingly let a vicious alien on board.

Aliens
Ripley (Sigourney Weaver), the sole survivor from the original Alien, is awakened after 57 years of drifting through space, her stories disbelieved by Company executives who tell her that the alien's planet is now inhabited and colonized. Once on the planet, no survivors can be found except for Newt, a little girl who awakens motherly instincts in Ripley just in time for the acid–blooded aliens to attack in what quickly becomes a one–sided battle for sheer survival.

Alien³
A penal colony and its inhabitants, a religious brotherhood of ex-convicts, is infiltrated by an alien when a ship carrying Ripley crash lands there.

Alien Resurrection
Ripley is brought back to life, from cloned DNA, by evil scientists who want to resurrect the alien that died inside her.