Sui compos (occasionally used as compos sui, but sui compos is the original), a Latin legal term describing a person who is deemed legally competent. The opposite is non sui compos.

The expression sui compos was used in Roman Law and typically continues to be used in legal systems derived from it (e.g., Canon Law as well as legal systems of many, though not all, European countries).

The exact definition of who is sui compos and who is non sui compos depends of the legal system, but usually two factors are involved: To be sui compos one has to be of a certain age, and one has to be sanae mentis, i.e., mentally sane.

The age is somewhat arbitrary (in that it is the same for everyone). It is not the same as the age of adulthood, but is typically much earlier. For example, according to Canon 97 of Code of Canon Law, before the completion of the age of 7 a minor is called an infant and is deemed non sui compos. Once the minor completes the seventh year, he is presumed to have the use of reason, and, thus, is sui compos.