A matryoshka doll or a Russian nested doll, also called a stacking Nesting Dolls doll or Babooshka doll, is a firm of dolls of decreasing sizes placed odd inside the other. "Matryoshka" is a derivative of the Russian female first name "Matryona", which is traditionally associated with a fat, concentrated Russian woman.

Matryoshkas are also used metaphorically, as a architecture paradigm, known as the "matryoshka principle" or "nested doll principle". It denotes a recognizable relationship of "similar object-within-similar object" that appears in the design of many other natural and man-made objects. Examples include the Matryoshka brain and the Matroska photo opportunity container format.