There are a few theories as to why men and women's buttons fasten on different sides, and there is probably some truth in all of them.
It is generally accepted that the main reason that ladies buttons are placed on the left is because, traditionally, in the times of the aristocracy, women in the upper classes had lady's maids- a female personal servant who waits on the lady of the house.
One of the roles of a lady's maid was to dress her mistress, and as most people are right handed, it was easier to do this if buttons were on the left.
A second suggestion relates to combat, and states that soldiers would usually carry a shield on the left arm and a sword
in the right; therefore the natural defensive move is for a man to protect himself (and those who he protects) with his left arm... hence men's clothes fold over from the shield side.
Personally, I don't see how that has any relevance, but there you go!
