For the comitia to be lawfully assembled, and for their acts to have the force of law, three conditions were necessary. First, the body or magistrate convoking them had to possess the necessary authority; secondly, the assembly had to be held on a day allowed by law; and thirdly, the auguries had to be favourable.

The reason for the first regulation needs no explanation; the second is a matter of policy. Thus, the comitia might not be held on festivals or market days, when the countryfolk, coming to Rome on business, had not time to spend the day in the public square. By means of the third, the senate held in check the proud and restive people, and meetly restrained the ardour of seditious tribunes, who, however, found more than one way of escaping this hindrance.

Laws and the election of rulers were not the only questions submitted to the judgment of the comitia: as the Roman people had taken on itself the most important functions of government, it may be said that the lot of Europe was regulated in its assemblies. The variety of their objects gave rise to the various forms these took, according to the matters on which they had to pronounce.