The Registro Mercantil is Spain’s official registry of companies (or Companies House). Their Electronic Registry has a version in English and is quite simple to use. To start, click on “card payments”. Once you pay with a credit card (under 5€ per consultation), you receive the basic information about a Spanish company, including the company’s tax ID, the director’s name, and the location of the physical office. You can have the information delivered online or sent to your email address.
If you need more detailed information about the company, you can ask for a certificate by going in person to the Mercantile Registry of the province where the company is registered. The main page of the Company Registry lists the addresses of the provincial offices and the central office in Madrid. You will also find information about the Property Registry.
When you form a company, the first step is to request a name from the Central Mercantile Registry. This is a good site to do a search for names for a new company, to search for regulations, and more. For some services you can pay by credit card, while others require electronic certification.