A panel unit used as part of a form for a concrete wall has a pair panels, held in spaced apart relation by a spacer. A spacer has rods with angled rod portions at the end which co-operate with other rod members to form retention cells which can receive reinforcement bar members. Another spacer is pre-fabricated in a generally planar grid with reinforcement members secured thereto. Connectors are used to connect the spacers to the panels. One type of connector is formed in two parts, with one part being removable, to permit removal of the panel, the other part having an anchoring mechanism. Another connector has a blade element enabling the connector flange to be recessed in the outer surface of the panel. A corner panel unit is also provided, as is a panel unit adapted for forming a wall with a ledge. In other panel units, form liners are provided which can permit a textured or contoured finished wall surface to be produced.