The New York Times recently featured my friend and doctoral classmate Hannah Riley Bowles' research on why women may earn less than men in part because of what occurs at the negotiating table. Bowles is a professor at Harvard's Kennedy School. She has found that women are less likely to request raises, and she notes, "We have found that if a man and a woman both attempt to negotiate for higher pay, people find a woman who does this, compared to one who does not, significantly less attractive."
What is so terrific about Bowles' research is that she has identified ways in which women can frame their requests so that they are much more likely to succeed in getting a compensation hike. Bowles finds that women should frame their requests in terms of the good of the firm as a whole, and they should make clear that they care about maintaining good relationships at work (while making their case on why a hike is deserved). They also must take care when using an outside offer as a bargaining chip, as this may cast them in a negative light - something men do not have to be concerned about as much.