The invention relates to a device and an assembly for cross-flow filtration comprising filter cassettes. Said filter cassettes are cost-effective to produce as they have few connections and simple clamping plates and are characterized by a long service life and by being highly flexible in adapting their capacity to the desired cross-flow filtration performance. The inventive device (1) comprises a holder and at least one filtration segment (2) consisting of clamping plates with filter cassettes fitted in a sealed manner therebetween. The clamping plates, which are configured as end plates, separation plates, distribution plates and collection plates and the filter cassettes are positioned on the holder so that they can be moved towards one another. The filtration segment consists of two sequences (3, 3) of at least one filter cassette (4, 4), a distribution plate (5, 5) and at least one additional filter cassette (6, 6), located between two end plates (7, 7) and interconnected by a common collection plate (8) for the evacuation of the filtrate. The device and assembly are used for treating liquid media in the fields of reverse osmosis, nanofiltration, dialysis, ultrafiltration and microfiltration.