Order posts in alphabetical order

I want to make an online glosary.
In every category section I want to order posts (words) in alphabetical order.

Example:
In main page first post has title “ab” and the second post “a” and the third post has title “ab”.
In category “A” I need an alphabetical order: first “a” second “ab” third “abc”….

How can I do this?
THX for your time ??