This chapter of the monograph "The Microbiology of the Atmosphere" by P. H. Gregory provides a historical overview of the study of airborne microorganisms, known as aerobiology. The text traces the development of understanding from ancient speculations about the origin of diseases to modern scientific methods for studying the air-spora. Key figures such as Lucretius, Anton van Leeuwenhoek, and Louis Pasteur are discussed, highlighting their contributions to the field. The chapter also covers the early work on the discovery of spores and the debate over spontaneous generation versus microbial origin. It details the pioneering efforts of Pierre Miquel and William Hesse in measuring and understanding the microbial content of the atmosphere, including the use of various sampling techniques. The historical context is placed within the broader narrative of the microbial theory of disease and the investigation of air-borne pathogens in relation to epidemic diseases. The chapter concludes with a discussion of the role of allergens and the impact of wind on the distribution of microorganisms.This chapter of the monograph "The Microbiology of the Atmosphere" by P. H. Gregory provides a historical overview of the study of airborne microorganisms, known as aerobiology. The text traces the development of understanding from ancient speculations about the origin of diseases to modern scientific methods for studying the air-spora. Key figures such as Lucretius, Anton van Leeuwenhoek, and Louis Pasteur are discussed, highlighting their contributions to the field. The chapter also covers the early work on the discovery of spores and the debate over spontaneous generation versus microbial origin. It details the pioneering efforts of Pierre Miquel and William Hesse in measuring and understanding the microbial content of the atmosphere, including the use of various sampling techniques. The historical context is placed within the broader narrative of the microbial theory of disease and the investigation of air-borne pathogens in relation to epidemic diseases. The chapter concludes with a discussion of the role of allergens and the impact of wind on the distribution of microorganisms.