In order to protect public order and morality, the shipment by post into Germany and the online commerce of publications including sound and vision media, data storage media, depictions and other representations of content that is likely to harm minors, or that is unconstitutional, is monitored.
Publications or media are harmful to minors if they are likely to endanger the process of educating children and adolescents and of developing socially responsible and self-reliant personalities.
The term unconstitutional publications refers to materials the content of which infringes on legally protected interests such as the free democratic order and the idea of understanding among nations, which discredit the symbols of the federal government, legislative or constitutional organs, or which may harm the reputation and operational readiness of the Armed Forces (Bundeswehr) or public security bodies (the Police, for example).

You will find more information in the "Import from a non-EU country" section.

Publications likely to harm minors and unconstitutional publications