A filter module (11) comprises a housing divided internally by a partition (14) into two compartments (15, 16). At least one hollow cylindrical filter element (12) is housed in one of the compartments, the or each filter element fitting about an opening (19) in the partition (14). A filter assembly (10) comprises a plurality of filter modules (11) mounted in a fluid flow line (13) such that incoming fluid enters one of the compartments, flows through the walls of the filter elements and filtered flow emerges from the other compartment.