The blanket sleeper (also known by many other synonyms and trade names) is a type of especially warm sleeping garment worn primarily during the winter in the United States and Canada. The garment is worn especially by infants and young children.

Typically, but not always, the blanket sleeper consists of a loose-fitting, one-piece garment of blanket-like material, enclosing the entire body except for the head and hands. It represents an intermediate step between regular pajamas, and bag-like coverings for infants such as buntings or infant sleeping bags (Terminology and Variations sections below). Like bag-like coverings, the blanket sleeper is designed to be sufficiently warm as to make regular blankets or other bed covers unnecessary, even in colder weather. Unlike such coverings, the blanket sleeper has bifurcated legs to allow unhindered walking (or crawling).

While no single feature is universal (see Terminology), distinguishing a blanket sleeper from regular pajamas usually include:

Although any sleeping garment with some or all of these characteristics could be called a blanket sleeper, the term is most commonly applied to a range of styles that deviate relatively little from the same basic design. (The features of this design are described in the Features section, below.)