The magnetic behavior of undoped (neutral), substituted poly(thiophene)s is reported. In particular, the influence of the nature of the substituent (alkyl, alkoxy, thioalkyl), the substitution pattern (head-to-tail (HT) versus head-to-head-tail-to-tail (HH-TT)), and the regioregularity oil the magnetic properties has been investigated. ESR spectroscopy reveals that the nature of the substituent determines the spin density, while the line width and asymmetry of the ESR signals are mainly governed by the substitution pattern and regioregularity. The spins give rise to a paramagnetic behavior. SQUID magnetometry reveals the presence of superparamagnetic order at room temperature, while ferromagnetism is observed at 5 K. The magnetic behavior observed by SQUID magnetometry does not (solely) originate front the ESR-active spin system. Its strength does therefore not depend on the ESR spin density, but seems to be governed by the supramolecular structure.