The need to shake hands before you dive into a negotiation sounds pretty obvious. But do you know the true power a handshake has over the results of that negotiation?

As a leader, you're aware of the power of first impressions. Setting the tone for a serious negotiation with millions of dollars at stake should be your first priority. Francesca Gino, an associate professor of business administration at Harvard Business School, says the first moments you meet someone are fundamental to how you feel about each other.

"People make inferences about one another's motives based on first impressions, which occur extremely quickly. We only need 100 milliseconds to form judgments of others on all sorts of dimensions, including likability, trustworthiness, competence, and aggressiveness," Gino writes in Harvard Business Review. "Even more interesting, our first impressions of others are generally accurate and reliable."

Studies have shown that shaking hands during a job interview--if you follow common advice like giving a firm grip and looking the other person in the eye--results in higher ratings of employment suitability. But in negotiations, the "message" a handshake sends is even greater. Gino conducted two studies relating to the handshake's effect during negotiations and found some convincing results.

"Consider that we all rely on subtle sources of information to determine whether to behave in cooperative or antagonistic ways during our negotiations. One such source of information is nonverbal behavior, including handshakes," she writes. "Across many cultures, shaking hands at the beginning and end of a negotiating session conveys a willingness to cooperate and reach a deal that considers the interests of the parties at the table. By paying attention to this behavior, negotiators can communicate their motives and intentions, and better understand how the other side is approaching discussions."

Gino's paper, "Handshaking Promotes Cooperative Dealmaking," cites multiple studies showing the importance of shaking hands. In one of them, she asked MBA students to negotiate as the buyer and seller in a mock real estate deal. She instructed half the pairs to shake hands before negotiating and did not give specific instructions to the other half.

"Most of them just jumped into the negotiation without shaking hands first, presumably because they were under time pressure. Pairs who had been asked to shake hands divided up the pie more evenly than did those in the control condition," she said. "In addition, buyers in the pairs who had been asked to shake hands were less misleading ... than were buyers in the control condition."

In another study, Gino and her colleagues randomly assigned students to the role of "hiring boss" or "job candidate" and gave them time to prepare for a negotiation of the latter's salary, start date, and office location. Half the pairs were told to shake hands, while the other half were seated immediately with no opportunity to shake. The study found that "shaking hands induced greater openness about negotiators' preferences on contentious issues and improved joint outcomes," she writes.

So the next time you have a big negotiation, remember to shake hands first. The result of that simple gesture may be in both parties' favor.