邀请信函(Invitation Letters)是邀请亲朋好友或知名人士、专家等参加某项活动时所发的邀约性书信。在国际交往以及日常的各种社交活动中，这类书信使用广泛。英文邀请信分为两种:一般邀请信和请柬(Invitation Card)。一般邀请信通常适用于一些平常的事情的邀请，而且邀请人同被邀请人之间很熟悉;请柬的格式严谨而固定，一般适用于较庄重和严肃的场合。
邀请信函的一般分类
一般来说，邀请信函可以分为邀请信和请柬两类。Generally, invitation letters can be divided into invitation letters and invitation cards.
1.邀请信(Invitation Letter)
邀请信可以是正式的，也可以是非正式的。正式的邀请信是用于重要的事务，如邀请一些杰出的专家、教授讲课;非正式的邀请信是用于个人交流,如邀请朋友参加聚会或晚宴，这样会显得更加亲切友好。
Invitation letter can be formal and informal. Formal invitation letters are issued only for important affairs , such as inviting some distinguished experts, professors to give lectures ; the informal ones are for personal communication like inviting friend for a gathering or dinner which look more personal and friendly.
2.请柬(Invitation Card)
请柬是一种最正式的邀请函，但长度很短，通常不超过14行。它注重对词的选择和对信纸的安排。由于格式的原因，请柬会用完整的名字代替缩写称呼也非常正式，如名字前通常要冠以先生和夫人。此外，请柬要用第三人称撰写，因此请柬上不能出现“我”或“我们”的字样。
The invitation card is a most formal invitation letter, though very short in length, usually less than 14 lines. It pays great emphasis on choice of words and the setup of letter paper. Due to its formality, the card would involve complete names instead of abbreviations, and salutation is very formal , for which Mr. and Mrs. are most preferred. In addition , the card is written in third person so that we do not use “ I” or“we” in invitation cards.
