Guild Wars 2

No. Sigils of the same type will not stack with each other.
Stacking on-kill sigils (like Bloodlust), which only allow a single stack (though switching out a weapon for a different sigil once you hit 25 is a good idea since they’ll stick around).
Also, every sigil with a cooldown (whether it be on-crit or on-weapon-swap) will share cooldowns, putting others on cooldown as well, which makes putting 2 on-crit sigils or 2 on-weapon-swap sigils on a waste (though you could have one of each and be functional, but they’ll still conflict with each other).

Yes you will, condition duration sigils stack.

You can also use 2 on-kill sigils at the same time to get 2 stacks per kill instead of 1 (as long as they are stacking the same effect and of the same power)

Dasorine.1964:

Yes you will, condition duration sigils stack.

You can also use 2 on-kill sigils at the same time to get 2 stacks per kill instead of 1 (as long as they are stacking the same effect and of the same power)

Oh. Huh, so condition duration stacks with itself but the other permanent buff sigils don’t. Didn’t see that part. Sorry about that one then.

gimmethegepgun.1284:

Dasorine.1964:

Yes you will, condition duration sigils stack.

You can also use 2 on-kill sigils at the same time to get 2 stacks per kill instead of 1 (as long as they are stacking the same effect and of the same power)

Oh. Huh, so condition duration stacks with itself but the other permanent buff sigils don’t. Didn’t see that part. Sorry about that one then.

Yeah I missed it first as well.

It comes with them seeming like the same thing (both sets are permanent increases to a certain thing) but end up actually being separate and really quite different. Strange how Anet does that on things.