The three citizen assemblies or Comitia, were called the Comitia Curiata, Comitia Centuriata and the Comitia (Plebis) Tributa (or Concilium Plebis or Populi Tributa). These were composed of all Roman male citizens, requiring individuals to attend in person, in order to vote. No debate from the floor was possible, and votes were counted in groups, not individually (the vote of each group was determined by the vote of the majority of individuals in that group). All 3 assemblies included the entire electorate of citizens, but each had a different internal organization (and therefore differences in the weight of an individual citizen's vote). In essence, each voting citizen had 3 potential votes, but each carried a different weight or responsibility.
Curiate Assembly (Comitia Curiata):
The oldest unit of organization within the Roman system. The 30 curiae of the early city (10 for each of the 3 early tribes), were based on clan and family associations. The Curiate was limited to Patricians as it reflected the oldest and most distinguished of the tribes. Each member had a single vote and the majority victor within each Curiate had 1 vote. Meaning, there were 30 separate votes with in each Curiate and the the Curiata as a whole would then have 1 vote to support its majority opinion. The Curiata became obsolete as a legislative body with the rise of Plebeian assemblies and further classifications of the nobility, but preserved its functions of endowing senior magistrates with imperium and witnessing religious affairs. The head of each curia was at least 50 years in age and elected for life.
Centuriate Assembly (Comitia Centuriata):
The most important of the Comitia units of organization within the Roman political system. There were 193 centuries, divided into 6 classes based on wealth and age which were originally reflective of military units. Membership in the classes was based on the capability to furnish armed men in groups of 100 (hence century). This group was controlled by the Patrician and Equestrian as the votes were weighted in favor of land owners and wealthy. The Centuriate elected censors and magistrates with imperium (consuls and praetors), was the proper body for approving the declaration of war; passed some laws (leges, sing. lex); and served as highest court of appeal in cases involving capital punishment.
Tribal Assembly (Comitia Plebis Tributa):
The Plebeian assembly was originally intended for the election of tribunes and deliberation of plebeians. The organization consisted of 1 urban tribe and 31 rural tribes, in which the membership was based on place of residence until 241 BC. From that date on local significance was largely lost and membership was based mainly on heredity. The Tributa (and later a subassembly, the Concilium Plebis) elected the lower magistrates (tribunes, aediles, quaestors). As it was simpler to convene and register 35 tribes than 193 centuries, it was more frequently used to pass legislation (plebiscites). Voting in favor of 31 less densely populated rural tribes; with presence in Rome required to cast a ballot, the assembly was controlled by landed aristocracy. Eventually became chief law-making body, as the laws of the Tribal assembly became binding on the entire state.