Starting this Friday, 27 Mar. until April 4, border checks will be in effect again for Germany and France.
Carrying a Passport or ID card (Personalausweis) will be necessary. It always is when crossing borders, but now they will be checked.
Border police are stepping up checks due to the up coming NATO meet in Strasbourg and Baden-Baden. Concerns are focused on violent protesters on there way to the meet. Seaports will also be under heightened scrutiny. Authorities are asking everyone to be patient at the borders because longer waits might not be avoidable.
For those that have lived in Europe for a few years, border checks have been a thing of the past since 1985 because of the Schengen Agreement. Exceptions can be made if there is a heightened security risk to the nation concerned.
Source: NATO-Gipfel: Bei Auslandsreisen Pass nicht vergessen! (Abendzeitung)