It is widely documented that infectious diseases have a very deep impact on numerous human populations. While public health campaigns have achieved spectacular successes, they do not appear to be evenly distributed throughout the world. Indeed, although many infectious diseases have been eliminated in the Western world, deadly pathogens are still spreading in many low-income countries. This chapter aims to describe the current epidemiological situations, reviewing control strategies and the progress that has been made in the fight against major human pathogens with the strongest impact in low-income countries. This chapter, therefore, introduces most of the pathogens that will be discussed in the book, and it describes why some epidemiological situations improved for some diseases more than for others.