In the Second Polish Republic, the legal status of illegitimate children was still regulated by the legislation of the invading states. Mostly, these were the regulations of the great civil codifications of the nineteenth century: The Napoleonic Code, The ABGB, The BGB, and also of the Civil Code of the Kingdom of Poland or of volume ten of The Digest of Laws of the Russian Empire. The author describes the legal status regarding the subject matter, including not only similarities but also differences among the legislations. The common feature of the regulations discussed was far‑reaching discrimination against illegitimate children in family law and inheritance law. Therefore, the Codification Commission of the Second Polish Republic faced not only the unification of the civil law, including family and inheritance law, in order to suspend the binding legislations of the invaders, but also to equalize the legal status of illegitimate children and legitimate children. Unfortunately, it was not possible to finalize the codification work on family law and inheritance law in the Second Polish Republic. However, these efforts were taken into consideration due to their later usage in the process of unification and codification of the civil law after the Second World War.