The journey to overcome one of the world’s most prevalent taboos is proof that no divide is impossible to bridge. This is the story of one woman’s path to create a grassroots effort that has now helped nearly 3 million women and girls in 145 countries on 6 continents—and isn’t stopping there. Every month, millions of girls and women around the world miss school and work during their periods because they don’t have access to menstrual products such as pads or tampons. In 2008, Celeste Mergens was working with an overcrowded orphanage on the outskirts of Nairobi, Kenya, when she learned that menstruating girls there sat on cardboard in their rooms for several days each month. This set into motion a seemingly simple idea—combining a washable, long-lasting pad with taboo-breaking health education—that became a catalyst for an unlikely global movement for equity. By creating opportunities and inclusive invitations for others to join, that movement grew to become the award-winning nonprofit Days for Girls. In this book, Mergens offers insight into what allowed her to face every obstacle with a positive mindset, determination, and humility. The challenges Mergens faced and the lessons she learned, personally and professionally, and the triumphs and resourcefulness of leaders all over the globe are illuminating to all who wish to make a difference and create a more equitable world. The Power of Days is a story of a social shift and a legacy for future generations—one that highlights the powerful impact we can have when we come together.