我们,咱们 both means: we, but when I should use 咱们， 我们？
What is the difference?
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There are already some answers there, but bare in mind the the use of the words may vary from place to place. – fefe Jun 9 '14 at 3:32
我们can be used both formally and colloquially across all Chinese speaking regions, while咱们appears more in spoken language and more in Northern China.我们may or may not include the listener, depending on the context, while咱们almost always includes the listener.Although
咱们includes both parties, there can be a strong or even exclusive focus on one party, either the speaker (e.g.瞧咱们的= "we'll show you how it's done") or the listener (e.g.咱们不怕= "let us not be afraid"). This type of usage is very common in Northern China but can be quite unfamiliar/unnatural to other Chinese speaking regions.
References:
[1] http://www.chiculture.net/0615/html/d16/0615d16.html
[2] http://www.fed.cuhk.edu.hk/~pth/pth_passage01.php?passage=99
"咱们" is more like a colloquial usage, especially in northern China(Beijing dialect makes extensive use of it, for example "咱几个"(roughly "we several people") ， "咱哥俩"(we two brothers).) While "我们" is the general written/spoken form and is commonly used all over China.
我们 and 咱们 can be used interchangeably，though 咱们 would less likely be used in formal writings. Because 咱们 is less formal, it makes the speaker seem more relatable to the person they are talking to (e.g 咱们俩是哥们，we are buddies).
