This chapter uses Malthus's Essay on the Principle of Population to provide a simple model of stagnation, which explains GDP per capita’s flat trend during the longest part of History. That model of Malthusian stagnation explains the constancy of standards of living as follows: during the longest part of History, each time a technological progress took place, this was followed by a rise in population size that annihilated any improvement in standards of living. As such, this chapter provides one possible representation of the stagnation regime. Criticisms of that theory of long-run stagnation by Marx, Weyland and others are also examined.