The following is from Medieval France: An Encyclopedia , eds. W. Kibler and G. Zinn. New York: Garland Publishing, 1995.

MEROVINGIAN DYNASTY. The first dynasty of kings to rule over the kingdom of the Franks became known as the Merovingians. Their realm included not only most of modern France, but also western Germany and the Low Countries. The first Merovingian to rule over this area was Clovis I (r. 482-511) and the last of the dynasty was Childeric III, who was overthrown by the Carolingian Pepin the Short in 751. The Merovingians are considered to be the "first race" of French kings, and their long retention of an old Germanic aristocratic hair fashion led to their being called "the long-haired kings." Their reputation is one of cruelty, violence, immorality, and fraticidal warfare. The term Merovingian is also applied to the entire period of Frankish history from 482 to 751, as well as to the culture and civilization of the lands under the control of the Merovingians.
The Merovingians are named for Merovech, a semi-legendary figure who was the father of Childeric I. Thus their origins are as chieftains of one of the many bands of Salian Franks living to the west of the lower Rhine, with their own center around Tournai and Cambrai, along the modern frontier between France and Belgium, in an area known as Toxandria. It is likely that all of the various Salian chieftains were related, and their power would have been that of prieSaint-judges. The Merovingians became true kings by two means. Childeric I, and perhaps Merovech before him, was an active ally of the Roman Empire and was himself a Roman official. Thus he would have been influenced by Roman concepts of kingship. Also, the takeover of the Roman administrative structure of Gaul by Clovis I put him in the legal position of the Roman emperor there. Thus from the beginning of the Frankish kingdom, in theory there were no constitutional restrictions on the power of the kings. The only limitation on their will was the willingness of their subjects to tolerate their actions. Merovingian kingship was, as it has been said, "absolutism tempered by assassination."
It was Clovis I who made the spectacular rise from being the leader of the Salian Franks around Tournai to becoming the founder of the Frankish kingdom. By warfare, deceit, and treachery he unified all of the Frankish tribes under his authority and conquered northern Gaul after his defeat of Syagrius in 486 and southern Gaul after his defeat of the Visigoths in 507. He also established his dominion over the Alemanni and the Thuringians. By the end of his reign in 511, Clovis ruled over a kingdom stretching from Germany to the Atlantic to the Pyrenees, in which the Franks themselves were only a small minority within a largely Gallo-Roman population. The Roman administrative structure was taken over intact by Clovis, and he worked closely with the Gallo-Roman aristocracy of his lands. The differences between Frank and Roman were further reduced by his conversion to orthodox Christianity.
These characteristics were continued after Clovis by his sons Theuderic, Chlodomer, Childebert I, and Clotar I. In accordance with Frankish custom, they received equal portions of their father's lands. Although there were then four independent Merovingian kingdoms, there was only one kingdom of the Franks. The next half century saw the conquest of the Burgundian kingdom by the sons of Clovis (534), but it also witnessed vicious warfare within the family that led to the extinction of the lines of three of the brothers and the reunification of the Merovingian kingdoms by Clotar I from 558 to 561. However, at his death, there was another quadripartite division of the kingdom among his sons, Charibert I, Sigibert, Guntram, and Chilperic I. Another half century of bloody warfare among the Merovingians ensued, and it was Chilperic I's son Clotar II who again reunited all the kingdoms (613). During this second major division, the four great distinct regions of the Frankish kingdom emerged--Neustria, Austrasia, Burgundy, and Aquitaine. They were to have a strong sense of identity as well as yearnings for autonomy. From time to time Austrasia received a son of the Merovingian king as an autonomous ruler. Yet with or without their own kings, Austrasia, Neustria, and Burgundy usually had their own royal administration under the direction of a mayor of the palace.
Clotar II and his son Dagobert I continued to rule in the strong Merovingian tradition. However, the rising power of the aristocracy, led by mayors of the palace, was already evident. After the death of Dagobert in 639, the position of the Merovingian kings declined rapidly and they fell under the domination of the aristocracy and the mayors of the palace. Merovingian reigns tended to follow the pattern of a weak or sickly king's death at an early age, leaving minor heirs under the tutelage of the magnates. The unification of the Frankish kingdom by Clotar II had the accidental effect of eliminating relatives as fellow kings, who in the past had served as guardians of such heirs. Also, the Merovingians often married low-born women who lacked powerful kinsmen who might have provided support for the queen and her children on such occasions. Moreover, generous land grants to favorites, especially aristocrats, had steadily reduced the material resources, and thus the power, of the kings.
The Merovingian kings after Dagobert I are traditionally seen as puppets of the mayors of the palace, as "do-nothing kings" (rois fainéants). It is true that the Merovingian decline tempted ambitious mayors like Ebroin of Neustria (d. 680) and Grimoald of Austrasia (d. 656) to plot to put up their own sons as kings, but aristocratic rivalries and strong loyalties to the Merovingian dynasty thwarted these efforts. Some of the later Merovingians were not mere puppets. Childeric II of Austrasia (662-75) was important enough to be murdered in a vendetta, and for a time Theuderic III (673-90/91) actually did rule rather than merely reign.
However, from the victory of the Austrasian mayor Pepin II in 687, the future of the Frankish kingdom was in the hands of the Pippinid-Carolingians. Charles Martel ruled without a Merovingian king on the throne from 737 to his death in 741, but the absence of a legitimate king provided an excuse for rebellions. Carloman and Pepin the Short were obliged to restore a Merovingian to the throne in 743. However, in 751 Pepin was secure enough to depose Childeric III and arrange his own election as king of the Franks, thus ending the Merovingian dynasty and inaugurating that of the Carolingians. The Merovingians did not die out. They were forcibly removed in a coup d'état. [Steven Fanning]

Gregory of Tours. History of the Franks , trans. Lewis Thorpe. Harmondsworth: Penguin Books, 1974.
Geary, Patrick J. Before France and Germany, The Creation and Transformation of the Merovingian World . London, Oxford, New York: Oxford UP, 1988.
James, Edward. The Franks . Oxford: Blackwell, 1988.
Wallace-Hadrill, J. M. The Long-Haired Kings . Medieval Academy Reprints for Teaching 2/ Toronto, Buffalo, London: U of Toronto P, 1982 (orig. 1962); ch. 7.