In Argentina, the DNI (Documento Nacional de Identidad) acts as a social security number; that is, it’s the personal ID you will often use to open a bank account and sign contracts for cell phones, cable service, internet service, and more. While there are still many things you can do without this number, you need it in order to prove that you’re an Argentine resident.
Argentina’s social security fund is called the Administración Nacional de la Seguridad Social, or ANSES. When you obtain a work visa, you will need to register with ANSES to get a CUIL (Código Único de Identificación Laboral) for pension purposes. A CUIL may be necessary for certain transactions, such as bank transfers or purchasing a car. However, you will not need to rely on this number for proof of identification; providing your DNI will normally suffice.
The steps for obtaining both a DNI and a CUIL are outlined in the ‘Visas’ section; see the page ‘You have a job and need to relocate’ for more.