For three hundred years, engineers have known that a sphere holding a true vacuum would rise through Earth's atmosphere — lighter than any gas-filled balloon, limited only by finding materials strong enough to resist atmospheric crush without adding weight that cancels the lift. EMPTY BALL argues that this limit has finally been reached. Built on classical shell-buckling mechanics, modern sandwich composites, and a guiding philosophy of "just enough" design, this book develops the Empty Ball System (EBS) from first principles into a working engineering concept. It covers adaptive spheres that expand with altitude, paired-hull architectures, oars that row both air and water, kite-based lateral thrust with no ground anchor, living-hull coatings for ships, and submerged floating roads for archipelago nations. The scope reaches beyond Earth's atmosphere to gentle-ascent space launch, intact orbital medical facilities, and subsea exploration of the ice-covered oceans of Europa and Enceladus. Part engineering reference, part manifesto for a different way of thinking about lift, buoyancy, and structure, EMPTY BALL works through the physics, the materials science, and the numbers behind each concept, chapter by chapter, without losing sight of why any of it matters. It is the second volume in a trilogy that began with Amber Gravity, continuing an inquiry into unconventional physics made practical.