Miss and Ms.

Miss- we usual call the lady who young or not yet marry
Ms- we usual call the lady who not yet marry and not young (haha!!) or devorce

2010-01-20 14:41:51 補充：
However, you have to becareful of those to call lady within their are willing. some lady love to be call Miss than Ms, although she is not girl anymore.

Miss-is not married
ms-is married

Miss 是指未 成親
Ms是指已成親

Women are getting more independent in these modern days so "Miss" means the woman is single, and "Ms." could be a single woman or a married woman. If you were to send a letter to someone and you weren't sure if the woman was married or not you would put "Ms. Smith." Also, some women today are also keeping their surnames after marriage (go by their surname and not their husbands last name) while others will link their surname with that of their new husbands. Eg: Her name is Smith and his is Johnson, so she'd go by "Mary Smith-Johnson." Some women will do this especially if they are in business.

"Miss" and "Mrs" are both contractions of "Mistress". "Ms", pronounced "mizz", appeared in the early 20th century as further contraction of both titles which is independent of marital status. [SOED 6th ed]

Ms. : 女士,
Miss: 小姐

Ms. -- put before the name of a woman, without making a distinction between married or unmarried status
Miss -- put before the name of a girl or an unmarried woman