
The constitution of the late Roman Empire was an unwritten set of guidelines and principles passed down, mainly through precedent, which defined the manner in which the late Roman Empire was governed. As a matter of historical convention, the late Roman Empire emerged from the Roman Principate, with the accession of Diocletian in AD 284, his reign marking the beginning of the Tetrarchy. The constitution of the Dominate ultimately recognized monarchy as the true source of power, and thus ended the fiction of dyarchy, in which emperor and Senate governed the empire together.

The Constitution of the Roman Empire was an unwritten set of guidelines and principles passed down mainly through precedent. After the fall of the Roman Republic, the constitutional balance of power shifted from the Roman Senate to the Roman Emperor. Beginning with the first emperor, Augustus, the emperor and the senate were theoretically two co-equal branches of government. In practice, however, the actual authority of the imperial Senate was negligible, as the emperor held the true power of the state. During the reign of the second emperor, Tiberius, many of the powers that had been held by the Roman assemblies were transferred to the Senate.

The Curiate Assembly was the principal assembly that evolved in shape and form over the course of the Roman Kingdom up until the Comitia Centurial organized by Servius Tullius. During these first decades, the people of Rome were organized into thirty units called "Curiae". The Curiae were ethnic in nature, and thus were organized on the basis of the early Roman family, or, more specifically, on the basis of the thirty original patrician (aristocratic) clans. The Curiae formed an assembly for legislative, electoral, and judicial purposes. The Curiate Assembly passed laws, elected Consuls, and tried judicial cases. Consuls always presided over the assembly. While plebeians (commoners) could participate in this assembly, only the patricians could vote.

The Dominate is the name sometimes given to the "despotic" later phase of imperial government, following the earlier period known as the "Principate", in the ancient Roman Empire. This phase is more often called the Tetrarchy at least until 313 when the empire was reunited.

The executive magistrates of the Roman Empire were elected individuals of the ancient Roman Empire. During the transition from monarchy to republic, the constitutional balance of power shifted from the executive to the Roman Senate. During the transition from republic to empire, the constitutional balance of power shifted back to the executive. Theoretically, the senate elected each new emperor, although in practice, it was the army which made the choice. The powers of an emperor, existed, in theory at least, by virtue of his legal standing. The two most significant components to an emperor's imperium were the "tribunician powers" and the "proconsular powers". In theory at least, the tribunician powers gave the emperor authority over Rome's civil government, while the proconsular powers gave him authority over the Roman army. While these distinctions were clearly defined during the early empire, eventually they were lost, and the emperor's powers became less constitutional and more monarchical.

The History of the Constitution of the Late Roman Empire is a study of the ancient Roman Empire that traces the progression of Roman political development from the abolition of the Roman Principate around the year 200 until the fall of the Western Roman Empire in 476 CE. When Diocletian became Roman Emperor in 284 CE, he inherited a constitution that was no longer functioning, and so he enacted the most significant constitutional reforms in over three-hundred years. His reforms, much like those three-hundred years before, were intended to correct the errors in the previous constitution. Diocletian's specific reforms were less radical than was the reality that he exposed the state of government for what it had been for centuries: monarchy. With Diocletian's reforms the Principate was abolished, and a new system, the Dominate, was established.

The history of the constitution of the Roman Empire begins with the establishment of the Principate in 27 BC and is considered to conclude with the abolition of that constitutional structure in favour of the Dominate at Diocletian's accession in AD 284. The Roman Empire's constitution emerged as a transformation of the late Roman Republic's constitution, utilising various late Republican precedents, to legitimise the granting of incredible legal powers to one man and the centralisation of legal powers into bodies which that man controlled.

The History of the Roman Constitution is a study of Ancient Rome that traces the progression of Roman political development from the founding of the city of Rome in 753 BC to the collapse of the Western Roman Empire in 476 AD. The constitution of the Roman Kingdom vested the sovereign power in the King of Rome. The king did have two rudimentary checks on his authority, which took the form of a board of elders and a popular assembly. The arrangement was similar to the constitutional arrangements found in contemporary Greek city-states. These Greek constitutional principles probably came to Rome through the Greek colonies of Magna Graecia in southern Italy. The Roman Kingdom was overthrown in 510 BC, according to legend, and in its place the Roman Republic was founded.

The legislative assemblies of the Roman Empire were political institutions in the ancient Roman Empire. During the reign of the second Roman Emperor, Tiberius, the powers that had been held by the Roman assemblies were transferred to the senate. The neutering of the assemblies had become inevitable for reasons beyond the fact that they were composed of the rabble of Rome. The electors were, in general, ignorant as to the merits of the important questions that were laid before them, and often willing to sell their votes to the highest bidder.

The Roman emperors were the rulers of the Roman Empire dating from the granting of the title of Augustus to Gaius Julius Caesar Octavianus by the Roman Senate in 27 BC, after major roles played by the populist dictator and military leader Julius Caesar. Augustus maintained a facade of Republican rule, rejecting monarchical titles but calling himself princeps senatus and princeps civitatis. The title of Augustus was conferred on his successors to the imperial position. The style of government instituted by Augustus is called the Principate and continued until reforms by Diocletian. The modern word 'emperor' derives from the title imperator, which was granted by an army to a successful general; during the initial phase of the empire, the title was generally used only by the princeps. For example, Augustus' official name was Imperator Caesar Divi Filius Augustus.

The Notitia Dignitatum is a document of the late Roman Empire that details the administrative organization of the Eastern and Western Empires. It is unique as one of very few surviving documents of Roman government and describes several thousand offices from the imperial court to provincial governments, diplomatic missions, and army units. It is usually considered to be accurate for the Western Roman Empire in the AD 420s and for the Eastern or Byzantine Empire in the AD 390s. However, the text itself is not dated, and omissions complicate ascertaining its date from its content.

Praeses is a Latin word meaning "placed before" or "at the head". In antiquity, notably under the Roman Dominate, it was used to refer to Roman governors; it continues to see some use for various modern positions.

The Principate is the name sometimes given to the first period of the Roman Empire from the beginning of the reign of Augustus in 27 BC to the end of the Crisis of the Third Century in 284 AD, after which it evolved into the so-called Dominate.

The Roman Assemblies were institutions in ancient Rome. They functioned as the machinery of the Roman legislative branch, and thus passed all legislation. Since the assemblies operated on the basis of a direct democracy, ordinary citizens, and not elected representatives, would cast all ballots. The assemblies were subject to strong checks on their power by the executive branch and by the Roman Senate. Laws were passed by Curia, Tribes, and century. When the city of Rome was founded, a senate and an assembly, the Curiate Assembly, were both created. The Curiate Assembly was the principal legislative assembly during the era of the Roman Kingdom. While its primary purpose was to elect new kings, it also possessed rudimentary legislative powers. Shortly after the founding of the Roman Republic, the principal legislative authority shifted to two new assemblies, the Tribal Assembly and the Centuriate Assembly. Eventually, most legislative powers were transferred to another assembly, the Plebeian Council. Ultimately, it was the Plebeian Council that disrupted the balance between the senate, the legislative branch, and the executive branch. This led to the collapse of the republic, and the founding of the Roman Empire in 21 BC. Under the empire, the powers that had been held by the assemblies were transferred to the senate. While the assemblies eventually lost their last semblance of political power, citizens continued to gather into them for organizational purposes. Eventually, however, the assemblies were abandoned.

The Roman magistrates were elected officials in Ancient Rome.

The Roman Senate was a governing and advisory assembly in ancient Rome. It was one of the most enduring institutions in Roman history, being established in the first days of the city of Rome. It survived the overthrow of the Roman monarchy in 509 BC; the fall of the Roman Republic in the 1st century BC; the division of the Roman Empire in AD 395; and the fall of the Western Roman Empire in 476; Justinian's attempted reconquest of the west in the 6th century, and lasted well into the Eastern Roman Empire's history.

The Senate of the Roman Empire was a political institution in the ancient Roman Empire. After the fall of the Roman Republic, the constitutional balance of power shifted from the Roman Senate to the Roman Emperor. Beginning with the first emperor, Augustus, the Emperor and the Senate were technically two co-equal branches of government. In practice, however, the actual authority of the imperial Senate was negligible, as the Emperor held the true power of the state. As such, membership in the senate became sought after by individuals seeking prestige and social standing, rather than actual authority. During the reigns of the first Emperors, legislative, judicial, and electoral powers were all transferred from the "Roman assemblies" to the Senate. However, since the control that the Emperor held over the senate was absolute, the Senate acted as a vehicle through which the Emperor exercised his autocratic powers.