Why do some companies ask for this? I can understand why a company would ask for your salary requirements, but why a salary history? I just had to make one because a job I was applying for said only resumes with salary histories will be considered. Is this so if they see you don't make a lot, then they won't pay you a lot either? I just don't see how it is fair for them to ask this. Also, it reminds me of the evil job agent from last week that told me that I can't go from what I'm making now to what I wanted to make (only 10,000 more and I am in a notoriously low paying field). I don't want people to consider my current salary when deciding how much they will pay me. I want to be evaluated fairly. I just want to understand why your current salary should have any reflection on what you deserve to be making. It makes me feel that if you take one low-paying job you are doomed to be paid a sucky salary forever.
In my experience, most places that require salary histories are trying to do the same thing as those who require salary requirements: find people who are making or who want to make what they want to pay. For this reason, I try to never use any specific numbers, I just say negotiable, or if they've given a range, say, 30,000-40,000, I actually state that as my range requirements. That way, I don't screw myself out of a higher paying job. I think it sucks of them to ask either question.