They mean the same thing; they can express : 1. necessity I have to go to work today. I must go to work today. 2. insistence You must try this new recipe. You have to try this new recipe. 3. To express an opinion that is very likely true: You must be hungry after working all day. You have to be hungry after working all day. That they mean the same thing is shown by the fact that "had to" is the past tense of "must." I must go to work today. I had to go to work yesterday. The exception to this is in reported speech, where "must" may also be used: The doctor said the patient must exercise more. = The doctor said the patient had to exercise more.

Both are obligations, but here's is the basic difference (you will also find this in English textbooks): "have to" = the obligation comes from outside; ie. someone else makes a demand, or the surrounding conditions cause the obligation "must" = the obligation comes from within; you do this because it's for your own good Because of this personal sense of "must", you may see the meaning transferred to mean a very strong obligation; as a negative it can signify a prohibited action. Alan has made a good point: you don't use "must"(as an obligation) in the past. Use "had to",

For example: Pupils must wear a uniform at school. (it's obligation) He has to get up at 7 because his school starts at 8.30. (it's need)

must = its a kind of advice but have to=obligation of course they have a lot of rules you MUST :) read them :)

"must" is used mostly to talk about the feeling and wishes, and "have to" is used mostly to talk about abligations that come from out side Example: I must keep my healthy. (It means want to) I have to keep my healthy, doctor's order.