A new and simple model is presented for an organic ferromagnet containing segregated stacks of radical ions. This new model gives a conceptual framework for selecting candidate molecules, and hence appears to be a promising, general guide for designing new organic ferromagnetic materials. The discovery of the first organic ferromagnet is reported. It is based on a polymer obtained from reacting s-triaminobenzene with iodine. The reaction is complex and the resulting polymer is not very reproducible. Nevertheless, on a number of occasions a ferromagnet material has been obtained. This material remains ferromagnetic to high temperatures, until it decomposes near 400°C. © 1987.