The chance of a successful pregnancy and healthy offspring is largely determined by the state of maternal but also paternal health during the periconception period, which starts at least 14 weeks before conception until 10 weeks afterward (12 weeks of gestation). Massive cell multiplication, differentiation, and programming processes of gametes and (extra) embryonic tissues during these 6 months around conception mean that these tissues are particularly sensitive for genetic and/or environmental exposures. Obstetric care mostly starts only at around 8–10 weeks of gestational age with a first ultrasound scan by a midwife or obstetrician, thereby missing the opportunity of prevention and treatment of harmful exposures, in order to optimize periconception health conditions. To emphasize the importance of preconception care, this chapter gives an overview of the biology of gametogenesis, embryogenesis, and placentation as determinants of the success of pregnancy course and outcome and health of the offspring during the life course. Because achieving a healthy lifestyle is one of the most important preventive measures in preconception care, the impact of maternal as well as paternal lifestyle on outcomes largely determined in the periconception period will be discussed.