Cynisca (/sɪˈnɪskə/; or Kyniska, Greek: Κυνίσκα; born c. 440 BC) was a wealthy Spartan princess. She is famous for being the first woman to win at the Olympic Games. Cynisca first entered the Olympics in 396 BC, where she won first prize competing with a team of horses she had trained herself. In 392 BC, Cynisca entered her horses in the Olympics for a second time and was awarded another victory in the same event.

The name Cynisca means 'female puppy' or 'little hound' in Ancient Greek. She was named after her grandfather Zeuxidamus, who was also called Cyniscos. Sarah B. Pomeroy suggest that this unusual name could have been a nickname for a tomboyish woman and it alludes to an interest in hunting. It is possible that the name is derived from the hunting traditions of the Spartan elite. Per Cartledge, it could have been a tribute to a species of a Spartan hound that was renowned as scenter during hunting. Pomeroy notes that the names of her close female relatives point to equestrian interests in their lineage.

Cynisca was born in the ancient Greek city-state of Sparta probably born around 440 BC. A member of the Eurypontid dynasty, she was the daughter of King Archidamus II and his wife Eupolia. She was probably half-sister to Agis II (r. 427–400 BC) and full sister to Agesilaus II (r. 400–360 BC), both of whom succeeded their father as a kings of Sparta. She had a sister named Proauga. In her childhood, Cynisca may have earned some experience in sporting from Sparta's female physical education curriculum (equivalent to boys' agoge), which she presumably attended. Coming from a wealthy family, she could own racehorses. According to Pausanias, Cynisca was the first woman to breed horses and was exceedingly ambitious to succeed at the Olympic Games.

Several sources from Xenophon and Plutarch mention how Agesilaus encouraged her to breed horses and compete in the games during her youth. However, his motivations for doing so have recently been debated. According to these ancient sources, Agesilaus supposedly viewed success in chariot racing as a victory without merit. Unlike other events, where a man's bravery and virtue were the decisive factors, he believed that chariot racing merely demonstrated wealth, as it required no direct involvement from the horses' owner. Both of these ancient authors suggested that Agesilaus hoped to expose how the sport was unmanly and aristocratic by having a woman win. Though in reality, Cynisca's victories did not stop wealthy Spartans from engaging in the sport. Several modern scholars, on the other hand, have theorized that Agesilaus' motivations were more practical. They suspect that he was using her victories and wealth to promote his own political career and gain public support through association, rather than providing a moral lesson. The evidence provided to support this theory is that Cynisca's two Olympic victories would have also brought fame to Agesilaus and to the wider Eurypontid house. Additionally, the establishment of Cynisca's hero-cult after her death could suggest that Agesilaus was still making use of his sister's fame even after her death.

In 396 BC, Cynisca employed charioteers to drive the horses she trained and entered her team at the Olympics for the first time, where it won in the four-horse chariot race (tethrippon Greek: τέθριππον). Cynisca is thought to have been approximately 40 years old when she won her first Olympic victory. In 392 BC, Cynisca again entered her racing team at the Olympic games and secured another victory.

To commemorate her Olympic achievements, Cynisca dedicated a set of bronze statues which depicted herself, her charioteer, her chariot, and her horses at the Temple of Zeus in Olympia. According to Pausanias, these statues were placed in a prominent location in the entrance way of the temple, next to the throne dedicated by Arimnestus, a king of Etruria. Along with the statues, Cynisca also celebrated her victories with an inscription, declaring that she was the only woman to win the wreath in the chariot events at the Olympic Games. Cynisca also dedicated another monument with copy of the same inscription in Sparta. The inscription from Olympia (c. 390-380 BC) reads:

Pausanias also mentions an epigram to Cynisca of unknown authorship, which he claims was the only poetic composition ever written to commemorate the deeds of the royal houses of the Lacedaemonians. In addition to this, a heroön (hero-shrine) was erected for Cynisca in Sparta at Plane-tree Grove, where religious ceremonies were held. Previously, only Spartan kings had been graced in this way; Cynisca was the first woman to receive this honor.

While most women in the ancient Greek world were kept in seclusion and forbidden to pursue athletic activities such as riding or hunting, Spartan women of the elite spartiate class were trained to excel in sports. The greater freedom that spartiate women experienced in terms of athletic pursuits was largely due to the fact that they were able to dedicate significant amounts of time to their training, since the helot system, whereby the majority of the population was kept in slavery, relieved them of the typical household duties that most other Greek women were expected to attend to. High levels of female athleticism were encouraged in Sparta because as a society, they believed that strong women would produce strong children and supply the army with powerful soldiers.