Le Roy Ladurie argued that the first wave, which was marked by the "low water mark" caused by the Black Death led to a period of economic and population growth. During this period, wages for labor fell, uncultivated lands and forests were converted into farm land, property was constantly divided and those who owned and managed their own land did well. The second wave, which Le Roy Ladurie called "the advance" which went until about 1530 and was marked by continued economic and population growth. After 1530, the "stubborn inelasticity" of French farming practices led to period of decline as farmers were unable to keep up with population growth due to a mixture of rigid farming practices, hostility to innovation, and inablitiy to obtain capital. During this period, people learned to live on less and married later in life, emigration increased, anti-tax revolts became common, belief in witchcraft increased and religious conflict between Catholics and Protestants led to a state of constant civil war.
The third wave, which Le Roy Ladurie calls "maturity," began in about 1600. This period saw the birth rate equalize with the death rate, and a decline of agriculture and capital accumulation caused by both a dramatic increase in taxes to the French Crown, tithes to the Catholic Church and loans to bankers together with conservative farming practices. The fourth wave was marked by general decline in living conditions and population caused by unemployment, late marriage, birth control, decreasing farm production, high emigration, and high taxes. During this "long period of recession" land was consolidated by a rural capitalist class. In Le Roy Ladurie's opinion society in Langudedoc ended more or less in the 18th century where it had began in the 15th century.
Le Roy Ladurie argued the determining feature of life in Languedoc was the culture of the people who lived there. Le Roy Ladurie maintained that the reason why the people of Landuedoc could not break the cycles of advance and decline was not so much caused by technological factors, but was due to culture that prevented the people from developing more progressive technology and farming practices. In Le Roy Ladurie's view, there were "structures" comprising long-term and slowly changing material and mental patterns which underlined the more dramatic and in Le Roy Ladurie's opinion less important "conjoncture" of trends and events which traditionally historians have focused upon. Like Braudel, Le Roy Ladurie believes that it is the history of the "structures" which really mattered, but unlike Braudel Le Roy Ladurie has expressed an interest in biography and the histoire èvènementielle (history of events) which Braudel dismissed as irrelevant.
His most noted work is Montaillou, village occitan de 1294 à 1324 (1975), a study of the village of Montaillou in the region of Languedoc in the south of France in the age of the Cathar heresy. In this work, he uses the meticulous notes of a member of the Inquisition, Jacques Fournier who served as the Bishop of Pamiers between 1318–1325 before becoming Pope Benedict XII, to develop a multi-layered study of life in a small French village over the course of several years. Le Roy Ladurie used the records of interrogations conducted by Fournier to offer a picture of both the material and mental worlds of the villagers. Le Roy Ladurie examined the former as reflected in farming practices, houses, relations with other villages and with both secular and ecclesiastical power and the latter as reflected in their beliefs about God, fate, sexuality, death, life, marriage, magic, space, time, and salvation.
Another noted work by Le Roy Ladurie was Le Carnival de Romans: de la chandeleur au mercredi des cenders (translated into English as Carnival in Romans) which dealt the 1580 massacre of about twenty artisans at the annual carnival in the town of Romans, France. In this book, Le Roy Ladurie used the only two surviving eye-witness accounts of the massacre (one of which was hostile towards to the victims of the massacre, the other sympathetic) together with such information as plague lists and tax lists to treat the massacre as a microcosm of the political, social and religious conflicts of rural society in later half of the 16th century France.
Other more recent treatments of social history by Le Roy Ladurie have included La sorcière de Jasmin (translated into English as Jasmin's Witch and Le siècle des Platter, 1499-1628 (translated into English as The Beggar and the Professor: a Sixteenth Century Family Drama). In Jasmin's Witch, Le Roy Ladurie following the lead of Carlo Ginzburg argued that the idea of witchcraft as seen by peasants was very different from the idea of witchcraft held by judges and churchmen. To understand the "total social fact of witchcraft", Le Roy Ladurie used an 1842 poem Françouneto written by Jacques Boè and based on a traditional French peasant folk tale. Le Roy Ladurie contended that the poem contains many authentic traces of popular beliefs about witchcraft in the 17th century-18th century rural France. Le Roy Ladurie argued that the "crime" of the "witch" Françouneto was the violation of the unwritten social code of "limited wealth", namely that she increased her own wealth at the expense of others. In The Beggar and the Professor, Le Roy Ladurie used the letters and memoirs of the Platter family to examine the social values of the 16th century, especially in regards to religion, medicine, crime, learning, and taxes.
Through best known for his work in "microhistory", Le Roy Ladurie has also examined the political history of France between 1460–1774. One of his best known political history books was L'Etat royal: de Louis XI à Henri IV, 1460-1610 (translated into English as The French Royal State: 1460-1610), Le Roy Ladurie traced the development of the French state between 1460–1610. In this book, Le Roy Ladurie argued that the major concerns of the French Crown were the economy, the Reformation and the aristocratic politics, and that the major reasons for the growth of the French state was military expansion into Italy, Provence and Burgundy and rivalry with Spain. In its sequel, Ancien Règime: de Louis XIII à Louis XV, 1610-1774 (translated into English as The Ancien Règime) Le Roy Ladurie argued that there was a close connection between the domestic and foreign policies of the French Crown. In particular, Le Roy Ladurie argued that periods of authoritarianism in domestic policy coincided with periods of aggression in foreign policy and that periods of liberalism in domestic policy coincided with periods of peace in foreign policy. Despite certain lapses in the 1750s, Le Roy Ladurie argued that the reign of Louis XV was characterized by liberalism at home and peace aboard while the rule of Louis XIV and Cardinal Richelieu were marked by aggression and authoritariansim. At the end of his two-volume history, Le Roy Ladurie stated that the growth of popularity of Enlightenment ideas, anti-clericalism, and liberalism had by 1774 already placed France on the road to the French Revolution.
Le Roy Ladurie is also known as one of the first modern environmental historians because his work focused on human agency in environmental change, as well as environmental factors in human history.
Without doubt one of the most prolific contemporary historians, his mentor was Fernand Braudel, a prominent member of the Annales School. At the beginning of the 1970s, Ladurie founded the movement of the "Nouvelle histoire" (New history). Le Roy Ladurie is and leading champion of "microhistory", in which an historian uses the study of an event, locality, family or life to reveal the "structures" which underlines life in the particular period under study. Some like Niall Ferguson have questioned the value of "microhistory" arguing that it is wrong to assume that the study of one village or one incident in one town or one family reveals wider patterns of life in France, let alone the rest of Europe. Another line of criticism has centered around Le Roy Ladurie's use of the term "structures" which his critics contend he has never clearly defined or explained why "structures" change over time or even if these "structures" Le Roy Ladurie purports to find even exist.
Le Roy Ladurie was a member of the French Communist Party (PCF) between 1945–1963, he left party after doubts caused by the 1956 Hungarian Revolution became too much for him. He has since then analysed his political engagement and Communist totalitarianism in Ouverture, société, pouvoir : De l’Edit de Nantes à la chute du communisme (2004) and Les grands procès politiques ou la pédagogie infernale (2002).
Emmanuel Le Roy Ladurie has also worked on the history of French regions (Histoire de France des régions, 2004) and on anthropometric history as well as on the impact of climate changes on human history. Besides writing books, Le Roy Ladurie is a prolific essayist writing on variety of subjects such as the utility of computers as method of historical research, rates of delinquency in the French Army in the 19th century, the spread of global diseases and the belief of French peasants that magic could be used to generate impotence. A major intellectual in France, Le Roy Ladurie often writes for the Le Nouvel Observateur, the L’Express, and Le Monde newspapers and often appears on French television.