enumerate tag using the alphabet instead of numbers

enumerate tag using the alphabet instead of numbers

The default behaviour for the \begin{enumerate}tag is to sequentially list
the items given by \item over the numbers {1, 2, 3, 4, ...}.
Is it possible to change this to the alphabet {a, b, c, d, ...}
How about Roman Numerals {i, ii, iii, iv, v, vi, ... }
How is this done?
Note that I use emacs 24.3. Thanks for all the help.