An ootheca /oʊ.əˈθiːkə/ (pl.: oothecae /oʊ.əˈθiːsiː/) is a type of egg capsule made by any member of a variety of animal groups such as mollusks, mantises, and cockroaches. It is also referred to by its shortened nickname, "ooth".

The word is a Latinized combination of oo-, meaning "egg", from the Greek word ōon (cf. Latin ovum), and theca, meaning a "cover" or "container", from the Greek theke. Ootheke is Greek for ovary.

Oothecae are made up of structural proteins and tanning agents^{[disambiguation needed]} that cause the protein to harden around the eggs, providing protection and stability. The production of ootheca convergently evolved across numerous insect species due to a selection for protection from parasites and other forms of predation, as the complex structure of the shell casing provides an evolutionary reproductive advantage (although the fitness and lifespan also depend on other factors such as the temperature of the incubating ootheca). Oothecae are most notably found in the orders Blattodea (cockroaches) and Mantodea (praying mantises), as well as in the subfamilies Cassidinae (Coleoptera) and Corinninae (Phasmatodea).

The ootheca protects the eggs from microorganisms, parasitoids, predators, and exposure. Its composition and appearance vary depending on species and environment.