A sex doll (also love doll or blow up doll) is a type of sex toy in the size and shape of a sexual partner for aid in masturbation.

The sex doll may consist of an entire body with face, or just a pelvic part, with the accessories (vagina, anus, mouth, penis) for sexual stimulation. The parts are sometimes vibrating and may be removable or interchangeable.

The dame de voyage (French) or dama de viaje (Spanish) was a direct predecessor to today's sex dolls that originated in the seventeenth century. Dames de voyage were makeshift masturbatory dolls made of sewn cloth or old clothes, used by French and Spanish sailors while isolated at sea during long voyages.

One of the earliest recorded appearances of manufactured sex dolls dates to 1908, in Iwan Bloch's The Sexual Life of Our Time. Bloch wrote:

In August 1955, Max Weissbrodt of the Hausser/Elastolin company created one of the first sex dolls to be marketed as such: an 11.5-inch plastic figurine named Bild Lilli, modeled after the hypersexualized appearance of a cartoon character named Lilli that had gained popularity in the German newspaper Bild Zeitung. Bild Lilli was marketed as a joke doll for "men who perhaps could not afford the real thing", advertised via pamphlets distributed to men who frequented German red-light districts such as Hamburg's Reeperbahn. Lilli dolls bore a striking resemblance to today's Barbie dolls.

In biology, sexual reproduction is a process of combining and mixing genetic traits, often resulting in the specialization of organisms into a male or female variety, each known as a sex. Sexual reproduction involves combining specialized cells (gametes) to form offspring that inherit traits from both parents. Gametes can be identical in form and function (known as isogametes), but in many cases an asymmetry has evolved such that two sex-specific types of gametes (heterogametes) exist: male gametes are small, motile, and optimized to transport their genetic information over a distance, while female gametes are large, non-motile and contain the nutrients necessary for the early development of the young organism.

An organism's sex is defined by the gametes it produces: males produce male gametes (spermatozoa, or sperm) while females produce female gametes (ova, or egg cells); individual organisms which produce both male and female gametes are termed hermaphroditic. Frequently, physical differences are associated with the different sexes of an organism; these sexual dimorphisms can reflect the different reproductive pressures the sexes experience.

A doll is a model of a human being, often used as a toy for children. Dolls have traditionally been used in magic and religious rituals throughout the world, and traditional dolls made of materials like clay and wood are found in the Americas, Asia, Africa and Europe. The earliest documented dolls go back to the ancient civilizations of Egypt, Greece and Rome. Dolls being used as toys was documented in Greece around 100AD. They have been made as crude, rudimentary playthings as well as elaborate art. Modern doll manufacturing has its roots in Germany going back to the 15th century. With industrialization and the appearance of new materials like porcelain and plastic, dolls were increasingly mass produced. During the 20th century dolls became increasingly popular as collectibles.

The earliest dolls were made from available materials like clay, stone, wood, bone, ivory, leather, wax, etc. Archaeological evidence places dolls as foremost candidate for oldest known toy. Wooden paddle dolls have been found in Egyptian tombs which date to as early as 2000 BCE. Dolls with movable limbs and removable clothing date back to at least 200 BCE. Greek dolls were made of clay and articulated at the hips and shoulders. There are stories from ancient Greece around 100AD that show that dolls were used by little girls as playthings. In Rome dolls were made of clay, wood or ivory. Dolls have been found in the graves of Roman children. Like children today, the younger members of Roman civilization would have dressed their dolls according to the latest fashions. When Greek and Roman girls got married they would dedicate their doll to a Goddess.Rag dolls are traditionally home-made from spare scraps of cloth material. Roman rag dolls have been found dating back to 300BC.