If multiple effects modify your hand size, apply them in timestamp order. For example, if you put Spellbook (an artifact that says you have no maximum hand size) onto the battlefield and then put Null Profusion onto the battlefield, your maximum hand size will be two. However, if those permanents entered the battlefield in the opposite order, you would have no maximum hand size.

If multiple effects modify your hand size, apply them in timestamp order. For example, if you put Null Profusion (an enchantment that says your maximum hand size is two) onto the battlefield and then put Venser's Journal onto the battlefield, you'll have no maximum hand size. However, if those permanents enter the battlefield in the opposite order, your maximum hand size would be two.