In the Preface and Introduction to London Labour and the London Poor, Mayhew introduces his ambitious project to document the lives and experiences of the lower classes in London. He highlights the need for more public knowledge about this population and aims to challenge prevalent 19th-century beliefs through the facts he presents. The author defends the accuracy of his work, acknowledging potential shortcomings but asserting his commitment to truthfulness. Mayhew explains the research he conducted over two years, interacting with thousands of individuals from the lower classes to gather their stories. He notes that he hopes his work will bridge the gap between the rich and poor, fostering empathy and inspiring action to improve the conditions of the less fortunate.

Mayhew divides humanity into two main categories: wanderers and settlers. Wanderers have nomadic lifestyles, while immigrants live in structured communities engaged in agriculture and other intellectual pursuits. Mayhew suggests that these divisions exist across different cultures and even in contemporary society. He then delves into the nomadic groups on London streets, categorizing them into distinct types such as sellers, buyers, performers, and artisans.