The term complementary feeding is defined as the period in which a progressive reduction of breastfeeding or infant-formula feeding takes place, while the infant is gradually introduced to solid foods. It is a crucial time in the infant’s life, not only because of the rapid changes in nutritional requirements and the consequent impact on infant growth and development, but also for a generation of lifelong flavor preferences and dietary habits that will influence mid and long-term health. There is an increasing body of evidence addressing the pivotal role of nutrition, especially during the early stages of life, and its link to the onset of chronic non-communicable diseases, such as obesity, hypertension, diabetes, and allergic diseases. It is clear that the way in which a child is introduced to complementary foods may have effects on the individual’s entire life. The aim of this review is to discuss the effects of complementary feeding timing, composition, and mode on mid and long-term health outcomes, in the light of the current evidence. Furthermore, we suggest practical tips for a healthy approach to complementary feeding, aiming at a healthy future, and highlight gaps to be filled.