Quod Erat Demonstrandum is a 2013 Romanian drama film directed by Andrei Gruzsniczki, starring Sorin Leoveanu and Ofelia Popii. It tells the story of two Romanian academics who are persecuted by Securitate, the secret police, in 1984. The title is a Latin phrase with the meaning "which had to be proven". The film is in black and white. It had a budget corresponding to 700,000 euro, of which 1.59 million Romanian leu came from the National Center for Cinema.

The film premiered at the Rome Film Festival where it won the Jury Special Prize. It won several other awards and was hailed as the best Romanian film of 2014 by several critics, but had fewer than 5000 admissions in its home country, which was seen as a disappointment.