Seyler & Tillemann was a Hamburg merchant bank in the 1750s and 1760s, that was owned by Abel Seyler and Johann Martin Tillemann. It involved itself in the currency market and "malicious" speculation with financial instruments during the Seven Years' War. It had ties to the brothers De Neufville in Amsterdam. Seyler & Tillemann went bankrupt as a result of the Amsterdam banking crisis of 1763 with 3–4 million Mark Banco in debts, an enormous sum. Its downfall also contributed to the downfall of other banking houses e.g. in Scandinavia.
