Many job postings ask you to include your salary history or your salary requirements when applying for the position. First of all, if the ad doesn't mention it, don't offer any salary information. If at all possible, you want the prospective employer to bring up the issue of compensation first.

Employers request salary information for various reasons. If your salary is too high, they can screen you out because they don't want to pay that much or because they think you won't be happy working for less money. If your current salary is lower than the company was planning to pay, they may offer you a lower salary.