In short: the cita previa de extranjería is the appointment you book to carry out in-person immigration procedures at the offices (Oficina de Extranjería, police station); you book it yourself on the official electronic headquarters and you do not need any paid intermediary.
In person or by representative? Booking the slot is online (you do it yourself on the electronic headquarters); you then attend the appointment in person at the office. In addition, many new authorisations and renewals are filed online via Mercurio, without an appointment.
The official channel is the Sede electrónica de Administraciones Públicas: sede.administracionespublicas.gob.es/icpplus. The appointment is used for many in-person procedures —among others, fingerprinting (toma de huellas) and issuance of the TIE, NIE assignment, residence and work authorisations, family reunification—. Booking the appointment is a public service; you should not pay anyone to "get" a slot. Any fees that exist (for example, the TIE fee) relate to the procedure itself, not to booking the slot. Be wary of anyone charging for or selling appointments: there is resale and even sale of fake appointments outside the official system. When the message "no hay cita disponible" appears, the official information explains that all appointments are currently taken; availability is managed by each office and slots are released periodically, so it is worth trying again later. In addition, many new authorisations and renewals can be filed online, without a cita previa, through the electronic headquarters (the Mercurio platform), which is the preferred option. To identify yourself you may need the NIE; and remember padrón registration as the basis for many procedures.
Steps:
- Go to the official site: sede.administracionespublicas.gob.es/icpplus.
- Choose your province and the procedure (fingerprinting/TIE, NIE assignment, etc.).
- Enter your details (NIE or passport) and pick an available slot.
- If "no hay cita disponible" appears, try again later (slots are released periodically); many renewals can be done online via Mercurio without an appointment.
Official source: Cita previa de extranjería — Sede electrónica de Administraciones Públicas and official FAQ on the immigration appointment. Informational only; check the official source and a professional for your specific case.