This article originally appeared at Inc.

Good leaders are constantly looking for ways to boost their employees’ sense of engagement and shared purpose. But you don’t need grand gestures to make people happier or more productive. In fact, the biggest payoff may come in small packaging.

The handwritten thank you note.

It’s a practice that has gained traction with executives at major companies. During his tenure as CEO of Campbell’s Soup, Douglas Conant delivered close to 30,000 handwritten notes to employees at all levels of the company, from senior executives to maintenance staff. Mark Zuckerberg made it his personal goal in 2014 to share one “well considered” thank you note with a Facebook employee each day. And Indra Nooyi, going one step further, even sent letters to the parents of top Pepsi executives.

Research shows that the simple act of expressing gratitude can literally change the way we feel. In one study, participants who spent ten weeks writing just a few sentences about things they were grateful for experienced greater optimism about their lives. Not only that, they also engaged in healthier behaviors, like exercising more regularly and getting more sleep.

Expressing gratitude can also boost productivity. Researchers at the Wharton School found that a group of university fundraisers who received hearty thanks from the school’s director of annual giving made 50 percent more fundraising calls than a second group that went unrecognized.

Gratitude in Action

When the leadership team at a major healthcare services provider asked me to help improve their internal culture, I suggested that senior executives take on a daily gratitude challenge for two weeks. At the start of each day, leaders spent several minutes making a short list of the people in the company who did something to impact them personally or improve the organization as a whole. Next to each name, they jotted down specific examples of what these individuals did and why it mattered.

For the next 10 to 15 minutes, leaders wrote thank you notes to each person on their list. One SVP thanked his assistant for keeping him up on track with his appointments. A sales director acknowledged the efforts of two members of her sales team who worked over the weekend to get a pitch ready by deadline. Much to the surprise and delight of the recipients, the notes–written on thick cardstock and packaged elegantly–were delivered in person by the leaders themselves.

Turns out a little gratitude goes a long way. In a follow-up conversation with leadership, I learned that the gratitude challenge had made such a splash that several employees began a campaign of their own. A few members of the marketing team created a “gratitude box” where employees could drop notes of appreciation singling out their colleagues for acts of kindness, support and above-and-beyond performance. The notes were read out loud at the start of a weekly team meeting, and the public recognition fostered goodwill among employees.  

Getting Going With Gratitude

A meaningful thank you note answers three big questions:

1. How did you help me? The most compelling expressions of gratitude are usually the most detailed. Be specific about what this person did to move you to write about it in the first place. Avoid generic statements or platitudes and reach for simple but heartfelt expressions of thanks.

2. What would life be like without that? Think about gratitude as a process of addition by subtraction. How might have things turned out without this person? What would be different about you or your life? When you start to imagine all the things that could’ve gone wrong, you won’t easily take for granted all the ways things went right.

3. Why did this matter? When someone helps us, we aren’t the only recipients. Think about others who might also have benefited from this person’s actions. List them and how their lives were improved as well. By recasting your gratitude in larger terms, the person receiving the note will experience a greater sense of satisfaction knowing that he or she made a difference on a grander scale.

Expressing gratitude can be difficult, and composing handwritten notes takes time and effort. But as research and experience has taught me, even small things can have big benefits.