邀请信包括宴会、舞会、晚餐、聚会、婚礼等各种邀请信件，形式上大体分为两种:一种为正规的格式 (formal correspondence)，亦称请柬；一种是非正式格式 (informal correspondence), 即一般的邀请信。邀请信是在形式上不如请柬那样正规，但也是很考究。书写时应注意:
邀请信一定要将邀请的时间（年、月、日、钟点）、地点、场合写清楚，不能使接信人存在任何疑虑。例如:“I’d like you and Bob to come to Luncheon next Friday.”这句话中所指的是哪个星期五并不明确，所以应加上具体日期, “I’d like you and Bob to come to luncheon next Friday, May the fifth.”
1. 邀请朋友共进午餐 Inviting a friend to informal luncheon
Dear [Zhang Ying]:
Will you come to luncheon on [Friday, May the fifth], at [twelve o’clock]?
My niece [Mary] is visiting us and I think you will enjoy meeting her. She is a charming, very pretty girl … and very good company! [John and Jane] will be here, and perhaps we can [give a dance] after luncheon. Do say you’ll come!