The eggs laid by modern birds are the products of more than 150 million years of evolution, resulting in a sophisticated package designed to balance a range of competing demands. The egg must be tough enough to prevent external damage but weak enough to permit a chick to hatch. It must resist bacterial contamination but allow gas exchange between the chick and the outside environment. The egg satisfies these requirements, which is remarkable given that it forms in under 24 hours. From an evolutionary perspective, bird eggs are fascinating because they come in a great variety of shapes, sizes, colors, and structures despite the fact that they serve the same essential function: to nourish and protect a chick until it hatches. What selective pressures influence the diversity of egg phenotypes? From an engineering perspective, eggshell is impressive because it is a strong, lightweight material, yet we understand relatively little about eggshell biomechanical properties outside of those from domestic chickens. What is the relationship between the structure and function of eggshell? In addition, how do eggs form in the avian oviduct? Here, we explore these questions through the lenses of evolutionary biology, biophysics and mechanical engineering, which together provide an integrative picture of the form and function of avian eggs.