This invention concerns a concrete side form system suitable for factory casting or site casting concrete. The side form (10) comprises a substantially rigid longitudinally extending wall. The wall has a first face to define the edge profile of a concrete panel poured onto a casting bed (16) bounded by the wall and a second face opposite the first face having formation to enable the wall to be secured to the casting bed. The wall comprises a longitudinally extending frame having formation along at least one of its edges to removably receive a removable longitudinal insert (13) to provide a shape along an edge of the concrete panel. The removable inserts (12, 13) provide the system with the ability to simply, easily and cost effectively change the edge profile of concrete poured against the side form. Architects can use the invention to specify standard or non standard edge profiles and achieve a much more diverse range of aesthetic finishes to the concrete edges without the cost beingprohibitive.