Can I renew my blue card even if my passport expired?
No, you generally cannot. Section 5 subsection 1 no. 4 of the Residence Act (Aufenthaltsgesetz) states the fulfillment of the passport requirement (according to section 3 of the Residence Act) as a general prerequisite to the granting of a residence title. And that section 3, subsection 1, reads: Foreigners may enter or stay in the federal territory only if they possess a recognised and valid passport or passport substitute, unless they are exempt from the passport requirement by virtue of a statutory instrument. Any statutory instrument which generally exempts regular Blue Card holders from the requirement does not exist. One exception could be that you home country, without proper reasons, refuses to issue a passport to you. In that case, you could apply for German substitute papers instead. The extension of a temporary residence permit follows the same rules as a first issuance (Section 8 subsection 1 of the Residence Act), and under section 4, subsection 1, second sentence of the Residence Act, the provisions applying to temporary residence permits also apply to EU Blue Cards. Furthermore, section 56 subsection 1 no. 1 of the Ordinance on Residence (Aufenthaltsverordnung) expressly requires third-country nationals to apply for a new passport that timely that it can be expected that a new passport will be issued before the current one expires. According to section 77 of the same ordinance, any intentional or negligent breach of this requirement is subject to a fine. Furthermore, any intentional breach of the passport requirement - stay in Germany without a recognised and valid passport - constitutes a criminal offence under section 95 of the Residence Act. This offence is construed to be a non-minor breach of a legal provision, which leads to a serious interest in expulsion according to section 54 subsection 2 no. 9 of the Residence Act. This public interest in expulsion then leads to the absence of a regular requirement for the issuance (or extension) of a residence title (section 5 subsection 1 no. 2 of the Residence Act). Thus, when the authorities establish that you intentionally stayed in Germany without a valid passport, and do not regard the case as atypical or exceptional (e.g. only a short period without a passport), you chances to get any renewal of the Blue Card are diminished even if you finally received a valid new passport, and they are - in any case, not only in cases of intention - zero if you cannot present one once you apply for the extension. So if someone has simply forgotten to check the validity, and the passport has expired without the holder having noticed it, the the best idea would be to apply for a new, perhaps an emergency, passport immediately and to present it as soon as possibly to the authorities. By the way, they record the validity of the passports presented to them in their files, so they know if someones passport had expired.