nice to meet you again：) 我们 is more formal , but you can use it both in writing and speaking. 咱们 is mainly used in some northeast provinces in China, such as Beijing and Shandong. It is a localism exactly. But basically all the mandarin speakers can understand if you say 咱们. BUT 咱们 can not use in formal writing. If you want to show a kindness to your chinese friend in speaking, do use 咱们！ all of 咱们 can be replaced by 我们 in all condition, but you can't do the opposite things.

The official difference is about something called "clusivity". Think about this example: WE'VE JUST WON THE LOTTERY! In this, you don't know if the person shouting this is telling the other person that he and his family/friends have just won the lottery, or if he is telling the person that he is talking to that they have won the lottery. European languages don't have this feature, but Chinese does, at least in the north. This word is essentially not used in the south or in Taiwan. 我們 means us (but doesn't technically include the person being spoken to, while 咱們 does. I hope that helps Laurence

They are totaly same. But咱们 is more informal and colloquial, it's also seemed like a kind of accent from especially north China.

usages: 1. While you can use 我们, usually, in a conversion, relates to the speaker and his people (not include the listener ) . Eg. (You're talking to your teacher about your trip to Beijing for example) "我们去了故宫、颐和园，还去了长城。" ---- we went to visit the Forbidden City, the Summer Palace, and the Great Wall. Apparently, your teacher didn't go. 2. In a "Let's go (or do sth)" circumstance, 我们=咱们, they're both used to suggest. Eg. (You and your friends have had a meal in a restaurant ) “我们/咱们走吧。” ----Shall we leave?/Let's go. "WE" both go. 3. we use 咱们 usually when the listener and speaker have very close relationship. Eg. （son persuades his parents） 咱们寒假去澳大利亚吧！ --- Let's go to Australia during the winter vacation! I want to go! PS. *There's an exception to 咱们 (in a store/shop...) -- "咱们这儿有德语书吗？" （Do you have German books for sell ？ ） -- “对不起先生，我们这儿没有德语的书。” （sorry sir, we don't sell German books.） Here, “咱们” is used to indicate the other side, especially when you buy something. Only used in daily life. :)

The main differences are mostly covered, there are 2 differences: 1) Dialect and Formality. "咱们" is basically a northern dialect and I think is used most intensively in the northeast. So it is not very formal and should not be used in essays. 2) Clusivity. "咱们" is an INCLUSIVE 'we', which means the speaker is including the listener as a part of the 'we' he/she is talking about. Whereas "我们" does not imply clusivity. It is like the English 'we', which can be either INCLUSIVE or EXCLUSIVE. It can go both ways.