1. 表示“关于”，注意与介词 on 的区别：about 指泛泛地或非正式地谈论某事，其谈论的内容也较为普通；而 on 则指比较有系统地或理论性较强地论述某事，其论述的内容较正式或较为严肃。试比较：
He was reading a book on ethics. 他正在读一本关于伦理学的书。
He wrote a book on scientific baby care. 他写了一本有关科学育婴的书。
She's writing a book on her travels in China. 她正在撰写一本有关她在中国旅行的书。
He has written a book about angling. 他写了一本关于钓鱼的书。
She had written a book about her childhood. (G51) 她写过一本关于自己童年的书。
He has been working on the illustration of a book about animals. 他一直在给一本有关动物的书画插图。
再比较：
(1) a book on rabbits 指的是一本论及兔子的学术著作
(2) a book about rabbits 指的可能是一本供小孩看的关于兔子的故事书
2. 表示“带在身上”，一般指随身带的小物品，有时可与表示类似含义的介词 with / on 换用：
He had a pistol about [on, with] him. 他身上带着一支手枪。
Have you got any money about [on, with] you? 你身上带钱没有?
How much cash do you have about [on, with] you? 你身上带着多少现金？
Do you have any identification / ID about [on, with] you? 你身上带着身份证件了吗?
3. 用于数字前，表示“大约”：
A generation is about 25 years. 一代大约是25年。
Please don't wake me till about 8. 请在八点左右才叫醒我。
I will call for you about 2.30. 我将在2点30分左右来接你。
I went to sleep about 11 last midnight. 我昨晚大约是在十一点睡着的。
4. 在动词 know, hear, speak 等之后用不用介词 about / of, 含义有差别：
I have heard about him, but I don't know him. 我听到过一些关于他的事，但不认识他这个人。
I've heard of him, but I don't know about him. 我听说过他，但我不知道有关他的情况。
比较：
know sb 认识某人
know of sb 知道有某人
know about sb 知道有关某人的事或情况
hear sb 听到某人（讲话）
hear of sb听说过某人
hear about sb 听到关于某人的事或情况
5. be about to (do)，意为“即将”“马上”。注意该短语不与具体的时间状语（如：soon, tomorrow, immediately 等）连用：
He was just about to burst into song. 他就要唱起歌来了。
Work was about to start on a new factory building. 新厂房即将动工。
I was about to leave when you came in, but I won't go now. 刚才我正要离开， 你就来了，我现在不走了。
Please buckle up now；we're about to land. 现在请系好安全带，我们就要着陆了。
比较正误句：
正：He is about to return to his homeland. 他即将回乡。
误：He is about to return to his homeland tomorrow.
另外注意：
(1) 该短语可与并列连词when（这时）连用：
I was (just) about to go to bed when the telephone rang. 我正要上床睡觉，这时突然电话铃响了起来。
(2) be about 之后可接动名词（但 be about to 之后不能接动名词）：
I was (just) about going to bed when the telephone rang. 我正要上床睡觉，这时突然电话铃响了起来。
