This box set collects multiple titles from the popular "What Is?" children's nonfiction series, published by Penguin Random House under the Who HQ imprint. Written by various authors, these illustrated books introduce young readers to history, science, geography, and culture through accessible, engaging storytelling. Each volume in the series answers a compelling question about a subject — from natural wonders and historical events to landmark inventions and cultural milestones — making complex topics approachable for readers ages 8 to 12.

The "What Is?" series is part of the broader Who HQ franchise, which also includes the bestselling "Who Was?" biography series. Books are designed for independent reading and are commonly used in classrooms and home libraries to supplement curriculum. This unit (U3) represents one themed grouping within the series lineup sold at Costco, and includes titles from Random House's curated selection of the most popular "What Is?" subjects.