Atypical pneumonia is a lower respiratory tract infection caused by pathogens that generally give rise to milder illness and result in less severe disease when compared with the typical agents of pneumonia. Respiratory complaints and systemic symptoms are rarely incapacitating and allow patients to continue their usual activities of daily living despite feeling unwell, illustrating why the illness is sometimes referred to as “walking pneumonia.” Atypical pneumonia is most commonly diagnosed in adolescents and young adults but can occur at any age beyond infancy. This chapter focuses on the patient characteristics, diagnostic approach, and treatment options for the five most common etiologic agents of atypical pneumonia.