Partition string into chunks

This seems like it should be trivial, but how do I partition a string into length n substrings? I can of course write something like

chunk[s_, n_] := StringJoin[#] & /@ Partition[Characters[s], n]

so that chunk["ABCDEF",2] -> {"AB","CD","EF"} but this appears unnecessarily cumbersome.

Answer

Try this:

StringCases["ABCDEFGHIJK", LetterCharacter ~~ LetterCharacter]

{"AB", "CD", "EF", "GH", "IJ"}

or for more general cases (i.e. not just for letters, but any characters, and for any partition size):

stringPartition1[s_String, n_Integer] := StringCases[s, StringExpression @@ Table[_, {n}]];

It is more elegant though to use Repeated (thanks rcollyer):

stringPartition2[s_String, n_Integer] := StringCases[s, Repeated[_, {n}]];

stringPartition2["longteststring", 4]

{"long", "test", "stri"}