The History of the Decline and Fall of the Roman Empire was written by English historian Edward Gibbon and published in six volumes. Volume I was published in 1776, and went through six printings. Volumes II and III were published in 1781; volumes IV, V, VI in 1788–89. The original volumes were published in quarto sections, a common publishing practice of the time. It stands as a major literary achievement of the 18th century because it was adopted as a model for the methodologies of modern historians. This led to Gibbon being called the first modern historian of Ancient Rome.

The books cover the period of the Roman Empire after Marcus Aurelius, from 180 to 1453. They take as their material the behavior and decisions that led to the decay and eventual fall of the Roman Empire in the East and West, offering an explanation for why the Roman Empire fell.

Gibbon is sometimes called the first "modern historian of ancient Rome." By virtue of its mostly objective approach and highly accurate use of reference material, Gibbon's work was adopted as a model for the methodologies of 19th and 20th century historians. His pessimism and detached use of irony was common to the historical genre of his era.

Although he published other books, Gibbon devoted much of his life to this one work (1772–1789). His autobiography Memoirs of My Life and Writings is devoted largely to his reflections on how the book virtually became his life. He compared the publication of each succeeding volume to a newborn child.

Gibbon offers an explanation for why the Roman Empire fell, a task made difficult by a lack of comprehensive written sources, though he was not the only historian to tackle the subject. Most of his ideas are directly taken from what few relevant records were available: those of the Roman moralists of the 4th and 5th centuries.

According to Gibbon, the Roman Empire succumbed to barbarian invasions in large part due to the gradual loss of civic virtue among its citizens. They had become weak, outsourcing their duties to defend their Empire to barbarian mercenaries, who then became so numerous and ingrained that they were able to take over the Empire. Romans, he believed, had become effeminate, unwilling to live a tougher, "manly" military lifestyle. He further blames the degeneracy of the Roman army and the Praetorian guards. In addition, Gibbon argued that Christianity created a belief that a better life existed after death, which fostered an indifference to the present among Roman citizens, thus sapping their desire to sacrifice for the Empire. He also believed its comparative pacifism tended to hamper the traditional Roman martial spirit. Finally, like other Enlightenment thinkers, Gibbon held in contempt the Middle Ages as a priest-ridden, superstitious, dark age. It was not until his own age of reason and rational thought, it was believed, that human history could resume its progress.

Gibbon sees the primary catalyst of the empire's initial decay and eventual collapse in the Praetorian Guard, instituted as a special class of soldiers permanently encamped in a commanding position within Rome, a seed planted by Augustus at the establishment of the empire. As Gibbon calls them at the outset of Chapter V: The Praetorian bands, whose licentious fury was the first symptom and cause of the decline of the Roman empire... He cites repeated examples of this special force abusing its power with calamitous results, including numerous instances of imperial assassination and demands of ever-increasing pay.

Gibbon provides the reader with a glimpse of his thought process with extensive notes along the body of the text, a precursor to the modern use of footnotes. Gibbon's footnotes are famous for their idiosyncrasies. They provide an entertaining moral commentary on both ancient Rome and 18th-century Great Britain. This technique enabled Gibbon to compare ancient Rome to modern times. Gibbon's work advocates a rationalist and progressive view of history.

Gibbon's citations provide in-depth detail regarding his use of sources for his work, which included documents dating back to ancient Rome. The detail within his asides and his care in noting the importance of each document is a precursor to modern-day historical footnoting methodology.