Heliaia or Heliaea (Greek: Ήλιαία; Doric: Ἁλία Halia) was the supreme court of ancient Athens. Τhe view generally held among scholars is that the court drew its name from the ancient Greek verb Ήλιάζεσθαι, which means συναθροίζεσθαι, namely congregate. Another version is that the court took its name from the fact that the hearings were taking place outdoors, under the sun. Heliaia was also called big ecclesia. Initially, this was the name of the place where the hearings were convoked, but later this appellation included the court as well.

The judges were called heliasts (Ήλιασταί) or dikasts (δικασταί, ὀμωμοκότες = those who have sworn, namely the jurors). The operation of judging was called Ήλιάζεσθαι (δικάζειν).

It is not clear whether Heliaia was instituted by Cleisthenes or Solon, but it seems that the latter initiated a function of the Assembly to sit as an appeals court. The court comprised 6.000 members, chosen annually by the lot among all the male citizens over 30 years old, unless they were in debt to the Treasury or disfranchised, namely deprived of their civil rights through the humiliating punishment of atimia (ἀτιμία). Those suffering from intellectual or corporeal flaws were also excepted, if their shortages prevented them from fully perceiving the proceedings. If any unqualified person participated in a jury, then information was laid against him and he was brought before the Heliaia. If convicted the court could assess against him whatever punishment or fine he is thought to deserve. If the punishment was a money fine, then the infringer had to go to prison until he had paid both the former debt, for which the information was laid, and whatever additional sum had been imposed on him as a fine by the court.