Shapeshifting Science Fiction

Shapeshifting is a popular and ancient trope in the speculative fiction genres. It has a history going back to epic poems such as the Iliad and can be found in the stories of many cultures. In science fiction the ability has a scientific explanation. For example, a gradual change in cellular alteration. These stories are about temporary physical transformation—a key defining attribute of shapeshifting is that its reversible. In sci fi the ability to change shape may belong to an alien race or it may be triggered by some technological invention.

Other Features of Shapeshifting Science Fiction

Level of Real Science
Moderate. Science is used to explain the shapeshifting ability; however, there are usually holes in the scientific explanation. For example, a creature becomes an elephant and then a mouse. A fun visual absolutely, but it ignores the issue of mass.
Level of Grand Ideas/Social Implications
Moderate. Shapeshifting stories tend to explore the same kinds of ideas that stem from the ability's propensity for revelation—the idea of the truth behind the facade, the beast hiding behind civilization, I?`deas of identity both personal and societal.
Level of Characterization
Moderate. The shapeshifter character is often more symbolic than individual—the character often represents a larger idea the story is attempting to convey. A classic example is Robert Louis Stevenson's Strange Case of Dr. Jekyll and Mr. Hyde. Jekyll is the epitome of civilization and Hyde is a beast, released by a scientifically brewed potion, who represents the constrained sexual and violent energies of the civilized man. In some ways, and in some stories, a shapeshifter is never really knowable—it can be a trickster and a deceiver, so readers never get a real sense of the character inside.
Level of Plot Complexity
Moderate. Shapeshifting can be used as a plot device—revealing the truth. It can also be used to inspire fear and make a plot feel more tumultuous—for example, in The Thing, the alien could be anyone, that makes for a very tense and tumultuous plot.
Level of Violence
Variable. Shapeshifting Sci Fi can be incredibly violent—monsters tearing apart and devouring their victims. Shapeshifting Sci Fi can also be relatively tame—when the character's shapeshifting ability manifests as the ability to stay young, it makes more of a medical story than a horror or action story.

Related Science Fiction subgenres

Alien Invasion Science Fiction. Aliens with the ability to assume human form.
Crossover Fiction. Shapeshifting is an ancient trope in Fantasy and Supernatural Fiction and is also used to inspire fear in Horror stories.
Speculative Fiction. The ability to shapeshift is also not uncommon in speculative fiction—sci fi just gives the ability a scientific explanation.
Age Regression Science Fiction. In some cases the ability to shapeshift is tied with getting younger.

Popular Shapeshifting Science Fiction Books

1 Who Goes There?

By John W. Campbell. In this classic Sci Fi tale that was adapted into film more than once as The Thing, an alien can eat and then replace terrestrial lifeforms.
2 Animorphs

By K.A. Applegate. In this YA series a group of kids have the ability to morph into any animal they have touched and acquired the DNA. They have been provided this ability by a race of advanced aliens.
3 Dune

By Frank Herbert. The Facedancer assassins assume the guise of other humans for the purposes of espionage and even assassination.
4 The Counterfeits

By Leo P. Kelley. Shapeshifting aliens have destroyed their own planet and set about doing the same to Earth—but it might not be intentional.
5 Find the Changeling

By Gregory Benford and Gordon Eklund. A bit of a thriller, this book charts the journey of two Earthmen to the planet of Alvea, where they hunt down the dangerous Changeling.
6 Majipoor

By Richard Delap and Walt Lee In this series the hostile alien, Metamorphs, are introduced in the book Shapes.
7 Darker Than You Think

By Jack Williamson. By a fluke of evolution a set of shapeshifters have split off from the human race and just might supplant them.
8 The Werewolf Principle

By Clifford D. Simak. The main character is a space traveler, with a bit of a memory problem and an alien problem—he shares his body with a wolf-like alien and a cybernetic consciousness.
9 Wild Seed

By Octavia Butler. The fourth book in the Patternist collection. This book is the story of a victim of alien abduction and enslavement because of her abilities (shapeshifting and others). It is an allegorical book about slavery in America.