The co-ownership is a type of company, formed by a private contract between two or more individuals, although is a possible legal form of company, has no legal personality as such. The tax regime is the income tax return (yield by economic activity) of each owner.
There is no minimum contribution to the co-ownership, and is not necessary to formalize a public document for its constitution, unless that provide real estate property or rights. The responsibility lies on the owners of co-ownership without limit.
Co-ownerships have a fiscal identification number (VAT Number), that they must request to the Tax Agency (AEAT), in order to make transactions and invoices with other companies.