A hen’s egg consists of an eggshell, eggshell membrane, egg yolk, and egg white, among which the egg yolk and egg white are consumed. Eggshells are usually discarded. The term eggshell is used to refer to the eggshell including the eggshell membrane, and both the eggshell membrane and the eggshell after removal of the eggshell membrane are known to exhibit health-promoting functions. The major component of the eggshell membrane is protein, and the major component of the eggshell after removal of the eggshell membrane is calcium (calcium carbonate). A characteristic feature of eggshells is their porous structure, and they are known to dissolve readily in gastric acid upon ingestion. Because dissolution by gastric acid is essential for absorption of dietary calcium, eggshells have attracted attention as a calcium source with high digestibility and bioavailability. High phosphorus intake inhibits calcium absorption, but eggshell calcium has low phosphorus content. This review discusses eggshell calcium’s health benefits: contributing to bone health (SOS in bone +40 m/s from baseline) and reduced blood pressure (systolic −8 mmHg, diastolic −4 mmHg from baseline). It also covers eggshell membrane’s absorbability, knee pain relief, and skin hydration improvement.