Before you start

A valid passport (sufficient for prepaid; an EU national ID is no longer reliably accepted by the big carriers since 2024 — bring a passport)
An unlocked phone (most are; eSIM-capable if you want to skip the physical SIM)
For a contract only: a NIE number and a Spanish bank account with an IBAN
For a contract only: a Spanish address (some providers also ask for your padró certificate)

Step-by-step

1
Decide prepaid vs contract
If you've just arrived and don't yet have a NIE or Spanish bank account, go prepaid — it needs only a passport. If you're settled with a NIE and a local IBAN, a contract or a fibre+mobile bundle is cheaper per GB and unlocks 5G and eSIM. Most newcomers start prepaid and switch later, keeping the same number via portability (portabilidad).
In personWho: YouSame day
2
Buy and register a prepaid SIM with your passport
Walk into any carrier store (Movistar, Vodafone, Orange) or value operator (Digi, Yoigo, Lowi, Simyo), or buy at a supermarket (Mercadona, Lidl), an estanco (tobacconist), or El Corte Inglés. Spanish law requires the SIM to be registered to an ID before activation, so staff scan your passport on the spot — no NIE required. Avoid airport kiosks (30-50% pricier). Digi's entry plan is ~€7 for 50GB with unlimited national calls and no commitment.
In personWho: You (carrier store, supermarket, or estanco)10-15 minutesFrom ~€7-15 for the first month/top-up
3
Top up (recarga) or set the SIM to auto-renew
Prepaid bundles renew every 28-30 days. Top up in the carrier's app, online with a card, at supermarket checkouts, ATMs, or estancos. Most value operators let you register the SIM to an online account so it auto-renews from a card. EU roaming works like home — your Spanish allowance covers travel across the EU/EEA at no extra cost (fair-use limits apply).
Mobile appWho: YouMinutesPlan price every 28-30 days
4
Switch to a contract or fibre+mobile bundle once settled
After you have your NIE and a Spanish IBAN, sign a monthly contract or — if you have a flat — a combined fibre + mobile bundle, which is markedly cheaper than buying each separately and is how most residents get cheap home internet. Ask for a tariff 'sin permanencia' (no minimum term) to stay flexible. Use portabilidad to carry your prepaid number across; it takes ~1 business day and is free.
OnlineWho: You (with carrier or MVNO)Number portability ~1 business dayMobile contracts ~€8-15/month; fibre+mobile bundles ~€20-40/month

Documents you’ll need

Passport (the reliable ID for prepaid registration; EU national IDs are patchily accepted since 2024)
NIE number (required for any contract, postpaid line, or fibre)
Spanish bank account / IBAN (required for the direct debit on a contract)
Spanish address, and sometimes a padró certificate, for contract billing

Things most newcomers don’t know

Prepaid is genuinely passport-only — no NIE — but it's NOT registration-free.

Spanish law forces the shop to tie every SIM to your ID before it activates. Newcomers assume prepaid is anonymous; in Spain you must hand over your passport at purchase, but you don't need the NIE that trips people up for contracts.

Source: Prepaid Data SIM Card Wiki (Spain)

Digi is the worst-kept secret among newcomers and budget-conscious locals: ~€7 for 50GB with unlimited national calls and zero commitment.

It massively undercuts Movistar/Vodafone/Orange, so starting on Digi prepaid (then keeping it or adding Digi fibre) is the default cost-saving move — just know Digi prepaid has no eSIM and no 5G.

Source: digimobil.es

EU roaming is 'roam like home' — your Spanish plan works across the EU/EEA at no surcharge (fair-use limits apply).

If your job involves travel around Europe, a cheap Spanish SIM doubles as your continent-wide plan, so there's little reason to keep a separate home-country line.

Source: European Commission — Roaming policy

eSIM exists from all four major operators, but not on most value-operator prepaid plans (Digi prepaid included).

If you want to activate a line online before you even land, you'll likely need a major carrier (or a travel eSIM); the cheapest MVNO prepaid still means picking up a physical SIM in person.

Source: Phone Travel Wiz — Digi Spain

Common mistakes to avoid

Trying to register a prepaid SIM with only a foreign national ID card — since 2024 the big carriers often reject these; bring your passport.
Expecting to sign a contract before you have a NIE and Spanish IBAN — the major providers strictly require both.
Buying your SIM at the airport — convenient but typically 30-50% pricier than the same plan in town or at a supermarket.
Getting locked into a 'permanencia' (minimum term) without realising — always ask for a tariff 'sin permanencia', especially on bundles.