證明書種類很多，有工作經歷證明、工作經驗證明、病情證明、留學生經濟擔保書、學業成績證明書等等，是用來證明一個人的`身份、學歷、婚姻狀況、身體情況等或某一件事情的真實情況。證明信的寫法通常也採用一般信件格式，但多省掉收信人的姓名、地址和結束用語。稱呼多用“To Whom It May Concern”意即“有關負責人”，但此項也可省略。寫證明書要求言簡意賅。
醫生證明書
Doctor's Certificate
June. 18, 2000
This is to certify that the patient, Mr. Tomas, male, aged 41, was admitted into our hospital on June. 9, 2000, for suffering from acute appendicitis. After immediate operation and ten days of treatment, he has got complete recovery and will be discharged on June. 19, 2000. It is suggested that he rest for one week at home before resuming his work.
Jack Hopkins
Surgeon-in-charge
醫生證明書
