In law, conversion is a tort where a party significantly interferes with an owner's immediate right to possession to a chattel by denying possession, damaging it, or destroying it. The damage caused by this control justifies the restitution of the chattel's full value.

Stealing something from someone else is one form of conversion. However, conversion is not limited to theft: conversion can also be accomplished by moving, transferring, discarding, hiding, vandalizing, or destroying another person's chattel. Merely using another person's chattel can be grounds for conversion in certain cases.

Remedy for conversion is usually in the form of damages equal to the value of the chattel. The convertor can return possession of the chattel to the complainant, but this is usually not required and can only be accepted in lieu of damages if the complainant agrees. If the complainant wants the chattel returned without any additional monetary damages, they can claim a related tort, detinue.

Conversion and other offenses

The definition of conversion overlaps with that of trespass to chattels: the primary difference between the two is that damages from a trespass claim are based on the harm caused to the plaintiff, rather than the value of the chattel. Many actions can constitute both conversion and trespass. In these cases, a plaintiff must choose which claim to press based on what damages they seek to recover.

Generally, the two torts are distinguished by:

1. how long, and to what extent, the tortfeasor exercises control over the chattel;
2. how long, and to what extent, the owner's rights are violated;
3. whether the tortfeasor acts in good faith;
4. the extent of harm to the chattel;
5. the extent of harm to the plaintiff.

Conversion should be distinguished from the taking of title or ownership. Neither of these principles of property apply as conversion deals only with physical possession of the chattels.