社交书信包括的内容很多，如邀请信、推荐信、介绍信、证明信、贺信、感谢信等等。写社交书信时切记如下几点：
(1)所有的社交书信都有明确的目的。因此，写社交书信时要一矢中的。
(2)不要写不相干的事。
(3)写上必不可少的事实，如时间、地点等。
(4)不要在一封信中将商务与社交混为一谈。
证明信(Certificate)
证明信包括下列几项：
(1)你是以什么资格了解被证明人或被证明公司的。
(2)你认识被证明人或被证明公司有多久了。
(3)被证明人或被证明公司的可靠性和能力如何。
【例一】
Euston UK LTD
8185 BARNLEY ROAD
DUNDEE
28th September, 1996
Ref: PVH/ltj
Jason ＆ Son Ltd.
Parkside Manor
Burnside
Dumfries
Dear sir：
Thank you for your letter of 20 September, requesting a reference for Clairish Computers Ltd. The answers to your questions are as follows:
1. We have employed Clairish Computers Ltd. since January 1995.
2. Clairish Computers has helped our company rectify a new computer system that had been badly installed by another firm of consultants. It has drawn up a system specification for a replacement system and has chosen appropriate hardware.
3. We did not select Clairish Computers from several candidates.
4. We were not first time computer users.
5. Our first system is working satisfactorily. The replacement system is still too new to comment on.
6. We are satisfied with the work of Clairish Computers. The various stages were completed on time, and the charges agreed with the quotes.
7. There was continuity of staff at Clairish Computers. Ian Baird managed the work, which was carried out by Alex Johnston and James MacReady.
8. The staff training was effectively carried out.
Yours faithfully,
Peter Haddon, Director
【例二】
Doctor’s Certificate
Oct. 18, 2000