Harold Adams Innis (November 5, 1894 – November 8, 1952) was a Canadian professor of political economy at the University of Toronto and the author of seminal works on media, communication theory, and Canadian economic history. He helped develop the staples thesis, which holds that Canada's culture, political history, and economy have been decisively influenced by the exploitation and export of a series of "staples" such as fur, fish, lumber, wheat, mined metals, and coal. The staple thesis dominated economic history in Canada from the 1930s to 1960s, and continues to be a fundamental part of the Canadian political economic tradition. Innis has been referred to as the "father of communications theory" and as the "father of Canadian economic history".

Innis's writings on communication explore the role of media in shaping the culture and development of civilizations. He argued, for example, that a balance between oral and written forms of communication contributed to the flourishing of Greek civilization in the 5th century BC. He warned, however, that Western civilization is now imperiled by powerful, advertising-driven media obsessed by "present-mindedness" and the "continuous, systematic, ruthless destruction of elements of permanence essential to cultural activity." His intellectual bond with Eric A. Havelock formed the foundations of the Toronto School of communication theory, which provided a source of inspiration for future members of the school Marshall McLuhan and Edmund Snow Carpenter.

Innis laid the basis for scholarship that looked at the social sciences from a distinctly Canadian point of view. As the head of the University of Toronto's political economy department, he worked to build up a cadre of Canadian scholars so that universities would not continue to rely as heavily on British or American-trained professors unfamiliar with Canada's history and culture. He was successful in establishing sources of financing for Canadian scholarly research.

As the Cold War grew hotter after 1947, Innis grew increasingly hostile to the United States. He warned repeatedly that Canada was becoming a subservient colony to its much more powerful southern neighbor. "We are indeed fighting for our lives", he warned, pointing especially to the "pernicious influence of American advertising ... We can only survive by taking persistent action at strategic points against American imperialism in all its attractive guises." His views influenced some younger scholars, including Donald Creighton.

Innis also tried to defend universities from political and economic pressures. He believed that independent universities, as centres of critical thought, were essential to the survival of Western civilization. His intellectual disciple and university colleague, Marshall McLuhan, lamented Innis's premature death as a disastrous loss for human understanding. McLuhan wrote: "I am pleased to think of my own book The Gutenberg Galaxy as a footnote to the observations of Innis on the subject of the psychic and social consequences, first of writing then of printing." Mel Watkins declared that Innis was "without doubt the most distinguished social scientist and historian, and one of the most distinguished intellectuals, that Canada has ever produced".

Innis was born on November 5, 1894, on a small livestock and dairy farm near the community of Otterville in southwestern Ontario's Oxford County. As a boy he loved the rhythms and routines of farm life and he never forgot his rural origins. His mother, Mary Adams Innis, had named him Herald, hoping he would become a minister in the strict evangelical Baptist faith that she and her husband William shared. At the time, the Baptist church was an important part of life in rural areas. It gave isolated families a sense of community and embodied the values of individualism and independence. Its far-flung congregations were not ruled by a centralized, bureaucratic authority. Innis became an agnostic in later life, but never lost his interest in religion. According to his friend and biographer Donald Creighton, Innis's character was moulded by the church:

The strict sense of values and the feeling of devotion to a cause, which became so characteristic of him in later life, were derived, in part at least, from the instruction imparted so zealously and unquestioningly inside the severely unadorned walls of the Baptist Church at Otterville.

Innis attended the one-room schoolhouse in Otterville and the community's high school. He travelled 20 miles (32 km) by train to Woodstock, Ontario, to complete his secondary education at a Baptist-run college. He intended to become a public-school teacher and passed the entrance examinations for teacher training, but decided to take a year off to earn the money he would need to support himself at an Ontario teachers' college. At age 18, therefore, he returned to the one-room schoolhouse at Otterville to teach for one term until the local school board could recruit a fully qualified teacher. The experience made him realize that the life of a teacher in a small, rural school was not for him.