Seyler & Tillemann was a Hamburg merchant bank in the mid 18th century, and was owned by Abel Seyler and . It notably involved itself in the currency market and 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 in debts, an enormous sum. Its downfall also contributed to the downfall of other banking houses e.g. in Scandinavia.