Anesthesia during pregnancy is challenging due to the extreme physiological and anatomical changes that occur. Deep knowledge of these changes and how they influence anesthesia is critical in order to offer safe anesthetic care to both, mother and the child. In this chapter, we will review the main features that occur in the respiratory, cardiovascular, central nervous, renal, and gastrointestinal systems, among others, and how it affects pharmacodynamics, pharmacokinetics, airway management and conduct of anesthesia. Fetomaternal circulation and fetal physiology focused on anesthesia will also be discussed.