In property law, a concurrent estate or co-tenancy is any of various ways in which property is owned by more than one person at a time. If more than one person owns the same property, they are commonly referred to as co-owners. Legal terminology for co-owners of real estate is either co-tenants or joint tenants, with the latter phrase signifying a right of survivorship. Most common law jurisdictions recognize tenancies in common and joint tenancies.

Many jurisdictions also recognize tenancies by the entirety, which is effectively a joint tenancy between married persons. Many jurisdictions refer to a joint tenancy as a joint tenancy with right of survivorship, but they are the same, as every joint tenancy includes a right of survivorship. In contrast, a tenancy in common does not include a right of survivorship.

The type of co-ownership does not affect the right of co-owners to sell their fractional interest in the property to others during their lifetimes, but it does affect their power to will the property upon death to their devisees in the case of joint tenants. However, any joint tenant can change this by severing the joint tenancy. This occurs whenever a joint tenant transfers his or her fractional interest in the property.

Laws can vary from place to place, and the following general discussion will not be applicable in its entirety to all jurisdictions.