Overlap

Most attribute increasing stats overlap in the world of Dungeons and Dragons.

Essentially what this means is that only the highest value in a given attribute is taken into account for calculations. Unless otherwise noted on the item or spell, things do not stack (are not additive with one another). Therefore it is of no use to attempt to stack all of one stat on any character via equipment or a spell.

(There is one obvious exception however. AC granted from Armor and shields stack and may stack with the highest +AC spell placed on the player along with base AC).