If multiple people are inventors of a patent, do you need the agreement of one of them or all of them to license the IP for that patent?

In the UK, as in almost all countries in Europe, a co-proprietor cannot grant a license under the patent, or assign the patent, without the consent of the other co-proprietors (unless there is a specific agreement between the co-proprietors stating otherwise). In most countries in Europe, a co-proprietor can however sue for infringement or work/exploit the invention themselves, without the consent of the other co-proprietors (again, unless there is a specific agreement to the contrary). I should also point out that in Europe, the proprietors of the patent, not the inventors, own the rights in the patent (of course, in certain cases the listed inventors may also be the listed proprietors).

In the US, individual inventors can assign or license the technology independent of the other inventor(s).