催款函是卖方在规定期限内未收到货款，提醒或催促买方付款的函件。
写此类催款函要求文字简练、意思清楚;同时要求语气诚恳、体贴，彬彬有礼。不可轻易怀疑对方故意拖欠不付，以免伤害对方感情，不利于达到索款的目的，或妨碍以后的业务。对于某些屡催不付，故意逃款的客户，语气则要强硬，措辞坚决。总之索款要把握一个原则:既要达到索款目的，又要与客户保持友好关系。
催款函常用表达如下:
The following items totaling＄4 000 are still open on your account.
It is now several weeks since we sent you our first invoice and we have not yet received your payment.
I’m wondering about your plans for paying your account which，as you know，is now over 40 days past due.
We must now ask you to settle this account within the next few days.Thank you for your cooperation in this matter.
In order to avoid the unfavorable impact on your reputation，please be sure to fulfill the payment of this before March 27.(www.xing528.com)
Sample
Dear Sirs，
It is very difficult to understand why we have not heard from you in reply to our two E-mail of 8th and 18th September for payment of the sum US＄80 000 you are still owing.We had hoped that you would at least explain why the account continues to remain unpaid.
I am sure you will agree that we have shown every consideration and now you fail to reply to our earlier requests for payment，I am afraid you leave us no choice but to take other steps to recover the amount due.
We are most reluctant to do anything from which your credit and reputation might suffer and even now we prepare to give you a further opportunity to put the matter right.We therefore propose to give you 15 days to clear your account.
Hope to see your cooperation in this matter.Thank you.
Yours faithfully，
Li Hua
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