Different is a word that is used with different prepositions: "different from", "different than", and "different to".
It is mostly speakers of American English who say "different than". Academic English dislikes it, on the not unreasonable grounds that no comparison is involved. The other two forms are both acceptable in British English; Fowler records that pedants may object to "different to" but on no real grounds.
- OED says (s.v than): "different(ly) than is not uncommon, esp. in the U.S., but continues to be regarded by many as incorrect", and s.v. different 1. b.: "The usual construction is now with from; that with to (after unlike, dissimilar to) is found in writers of all ages, and is frequent colloquially, but is by many considered incorrect. The construction with than (after other than), is found in Fuller, Addison, Steele, De Foe, Richardson, Goldsmith, Miss Burney, Coleridge, Southey, De Quincey, Carlyle, Thackeray, Newman, Trench, and Dasent, among others."
There is also a usage of different as an absolute, without making a comparison, as in "he's so different". In this context it means 'special' or 'unusual'. OED says this is a colloquialism; you should avoid it in academic writing.