A creasing machine (1) for forming creases in sheets (11) of flexible material, said creasing machine (1) including a creasing mechanism (5), a transport mechanism (3) for transporting sheets (11) of material through the creasing mechanism, and a control means (7) for controlling operation of the creasing mechanism (5) and the transport mechanism (3), said creasing mechanism (3) including first and second creasing members (25,27) and a drive mechanism (28) for driving the creasing members (25,27), wherein the creasing members (25,27) are arranged to move in the direction of movement of the sheet (11) and at least one of said creasing members (25,27) is moveable towards the other creasing member (25,27) to produce a crease in a sheet (11) located between those members (25,27), and wherein the control means (7) is arranged to substantially match the speed of movement of the creasing members (25,27) with the speed of the sheet to enable the sheet to be creased while moving.