For example, if I have glass gauntlets that increase bow damage by 38%, and a pair of rings that increase bow damage by 20%, do the effects stack and thus I do 58% more bow damage? Or does it only take the highest value?

Pretty sure they stack

They do stack. You can for instance fortify destruction 25% on four different pieces of equipment and be able to cast destruction magic that costs 0 magicka,

They stack, potions unfortunately, do not.

They stack.  I was wondering where you could get the most petty soul gems?

@spazmaster666 said:

They do stack. You can for instance fortify destruction 25% on four different pieces of equipment and be able to cast destruction magic that costs 0 magicka,

If you get Fortify Destruction over 100%, do you gain mana by casting Destruction spells?

@Ravenlight said:

If you get Fortify Destruction over 100%, do you gain mana by casting Destruction spells?

No, but it would be pretty funny if it did. I tested all the fortify (spell school) enchantments by setting my enchantment skill to 500 in the console so that I get like decrease casting cost by -379% but all it does is make all the spells cost 0 magicka.

They stack, but as a word of caution some things seem to be glitchy with enchantments.

For example, I have gloves, a blacksmith apron, and a silver ring and necklace all enchanted +20% to smithing.

When I equipped them all directly from he chest where I keep them (without moving it to my inventory first, THEN equipping) it didn't give me the effect. When I unequipped and reequipped the stuff, it did.

By the way, it seems like you can damned near break the game with some of the enchanting stuff. Like between Sneak perks, Muffle, and enchanting + to sneak on everything that can take it you could be basically invisible.

@Robo said:

By the way, it seems like you can damned near break the game with some of the enchanting stuff. Like between Sneak perks, Muffle, and enchanting + to sneak on everything that can take it you could be basically invisible.

Well thats always been the case in elders scrolls. Chameleon in oblivion for example.

@TheDudeOfGaming said:

They stack, potions unfortunately, do not.

What about potions of different, but related types? Like what happens if I drink a resist magic potion and a resist fire potion, and then someone casts a fire spell on me?

Yes. I'm pretty sure there's a magic resistance cap of 85%, but you should be able to increase anything else for as many points as you can find to put into stuff