Shapeshifting is the ability of werewolves and hybrids to change one's shape. More specifically, into a supernatural wolf. To werewolves, this power is activated involuntarily every Full Moon unless they develop it by wearing Moonlight Rings or evolving. For hybrids, this power can be activated at will.
During a full moon, they will unwillingly transform from their human form into their wolf form. However, if a female werewolf is pregnant, they will not turn for nine months as the transformation would kill the baby. There are ways to induce this trait outside of the Moon's influence. Such ways would be to become a Hybrid, through the possession of a Moonlight Ring or performing a unification ceremony. These three are so far the only known methods of voluntarily controlling a Werewolf's transformed state.
Non-original Hybrids and Klaus have the ability to transform into their werewolf forms at will. Most of them avoid transforming at all due to the pain it causes.
They still, however, have no control of their actions in werewolf form. They can also perform partial transformations, manifesting single features of their werewolf forms.
Elijah informs Klaus that he remained a werewolf for 2 days, even when the sun was up. Showing that a non-original Hybrid and Klaus can stay in Werewolf form longer than a normal Werewolf.
As seen with Klaus when he bit Katherine, a non-original hybrid and Klaus can transform partially, displaying their werewolf eyes and teeth. When a female werewolf is impregnated, they do not transform for nine months, or until the baby is born.