Herbarium is a fascinating enquiry into this unique field of plant biology, exploring how herbaria emerged and have changed over time, who promoted and contributed to them, and why they remain such an important source of data for their new role: understanding how the world’s flora is changing. Barbara Thiers, director of the William and Lynda Steere Herbarium at the New York Botanical Garden, also explains how recent innovations that allow us to see things at both the molecular level and on a global scale can be applied to herbaria specimens, helping us address some of the most critical problems facing the world today.