With a normal bank account, you are the sole owner, and therefore it’s pretty straightforward in regards to who can and cannot move the money around. It’s just you.
But with a joint account, two or more people are equal owners of the account, and therefore of the money within it. So things can get a little more complicated, especially if there are any disagreements at any given point. 
If you have a joint account, then it is not illegal to withdraw money from it. Although it doesn’t just belong to you, it does belong to you, and you all get equal access to it, meaning all of the joint owners have equal capabilities for withdrawing money from the account.
This is why it is super important to make sure you fully trust the person or people before you open a joint account with them. It’s a pretty serious affair, and you should always be 100% sure before committing to it.
However, when opening a joint account, every single person involved will have to sign a mandate, where all the rules and legal obligations are stated.
During the process of opening a joint account, it can be decided whether permission is needed from all the joint owners or not, when it comes to withdrawing money.
So you could have the joint account so that every owner has to approve the money withdrawal before it is allowed, or you could have it so that any of the owners of the joint account can withdraw money at any point without the need for approval from the rest.
As long as you are following the mandate, then it is perfectly legal for you or any other owner of the joint account to withdraw money. After all, it belongs to all of you equally!
So…what if you have a problem with the other joint owner of the account, like for example a bad breakup or a massive argument? In this scenario, you should quickly cancel the mandate.
This will cause the account to freeze up, and it will mean that nobody can withdraw any money from the joint account until a formal agreement is reached between the joint owners as to who gets what money and how everything is handled.
The answer to this is yes. Any person within the joint account can both deposit and withdraw money, as well as perform transactions. Sometimes, it is established during the creation of the joint account that permission is needed for these actions.
But most commonly, the mandate does not state that permission is required, and so any of the joint owners can freely take all the money out at any given time.
This is why it is so important to fully trust the person or people you are opening a joint account with.
It is a serious commitment, and they could legally take all the money out of the joint account, even if you were the one depositing most of the money, and there’s nothing you could do about it, as you are both equal owners of the money within the joint account.
If you fear or suspect that the other person is going to take all the money out, perhaps due to a bad fall-out or disagreement, then you should immediately contact the bank and cancel the mandate, so that the joint account is frozen and nobody can withdraw any money or perform any transactions.
Once this is done, a formal agreement between all the joint owners will be needed in order to unfreeze the account, in which you can agree upon who takes what amount of money, and other details.
You can definitely sue someone for taking money out of a joint bank account, but the lawsuit has a very small possibility of being successful.
This is because the other person is legally allowed to withdraw the money freely, as you are down as joint owners, and therefore have committed to trusting one another in regards to the money within the account.
However, in some cases, depending on the situation, the circumstances, and the amount of money that was taken out of the joint bank account, a judge might rule in your favor and you might be able to get a small portion of the money back.
(But you will not be able to get it all back, no matter who deposited the money, it belongs to both owners equally.)
When creating a joint bank account, both signatures will be needed in order to agree on the mandate and to legally commit to the joint account and all its rules.
After that, both signatures will only be needed if the mandate requires permission from both owners in order to approve certain transactions or money withdrawals.
