Who needs one
Every foreign founder, director and corporate founder involved in a Croatian company needs an OIB. Foreign individuals and foreign companies are both assigned one.
How to get it
In person or through a representative
The application is filed with the competent office of the Croatian Tax Administration, either in person or through an authorised representative. Individuals provide a passport or an EU identity card. Foreign companies provide a registry extract in Croatian or with a certified translation.
Online, for EU/EEA citizens
EU/EEA citizens with valid credentials for the e-Citizens system can request an OIB online.
Using a representative
The power of attorney must be specific to the OIB procedure and written in Croatian or translated into Croatian. Whether it must be certified depends on who the representative is: authorisations given to a notary, attorney, tax adviser or bank do not need certification, while those given to other individuals or companies do.
The OIB confirmation proves your number. It is not an identity document.
Source: Croatian Tax Administration (porezna-uprava.gov.hr), pages on assigning OIB numbers.