An insulated siding panel comprises a foam insulation layer, an attachment member, and optionally a veneer layer. The foam insulation layer comprises a front face, a rear face, a tongue along a first end edge, a groove along a second end edge, and a slot defined in the rear face. The attachment member comprises an attachment rail and a member extending transversely from the attachment rail. The member of the attachment member is inserted into the slot of the foam insulation layer. When present, the veneer layer is attached to the front face of the foam insulation layer. When joined with other insulated siding panels, the interlocking occurs along the foam insulation layers to form an unbroken layer of insulation.