A Kellett motion is a motion to dismiss a current case because a prior case was already adjudicated and the new case should have been presented then. It gets its name from Kellett v. Superior Court (1966) 63 Cal.2d 822.

In 1966, the California Supreme Court issued its holding in a landmark criminal procedure case:

“If needless harassment and the waste of public funds are to be avoided, some acts that are divisible for the purpose of punishment must be regarded as being too interrelated to permit their being prosecuted successively. When there is a course of conduct involving several physical acts, the actor’s intent or objective and the number of victims involved, which are crucial in determining the permissible punishment, may be immaterial when successive prosecutions are attempted. When, as here, the prosecution is or should be aware of more than one offense in which the same act or course of conduct plays a significant part, all such offenses must be prosecuted in a single proceeding unless joinder is prohibited or severance permitted for good cause. Failure to unite all such offenses will result in a bar to subsequent prosecution of any offense omitted if the initial proceedings culminate in either acquittal or conviction and sentence.”

(Kellett v. Superior Court (1966) 63 Cal.2d 822, 827 [48 Cal.Rptr. 366, 409 P.2d 206].)