The in ovo technique is a method where nutrients are injected into the egg during embryonic development. This method has been developed especially in poultry farming in order to meet the nutritional needs of the embryo, to improve its development and to obtain healthier and stronger birds after hatching. In in ovo feeding, carbohydrates, fats, amino acids, minerals, vitamins, and other additives are used. The injection is performed in five egg regions: the air cell, allantoic sac, amniotic fluid, embryo body, and yolk sac. Studies have reported that in ovo injection affects various parameters, such as the embryo's age and hatchability. The timing of the injection varies depending on the region being injected, but it is generally performed during the embryo's hatching period. Evaluating the results of studies conducted considering the needs during the embryonic period, in ovo feeding has been reported to improve post-hatch parameters in animals. Additionally, the in ovo feeding application strengthens the chicks' intestinal development and immune system during the embryonic period, allowing them to store more nutrients when they hatch. However, it has been reported that in ovo carbohydrate feeding does not show an entirely positive effect on meeting the energy needs of the embryo and improving hatchability parameters. In ovo, amino acid feeding has been found to increase the absorption capacity of the intestine during the embryonic development process, increasing hatch weight. The effects of in ovo fat feeding on growth, development, and immunity are unclear. In ovo, vitamin feeding has been found to protect the embryo against oxidative damage that occurs as a result of metabolism or when exposed to heat stress during embryo development, as well as improve hatchability parameters. In general, it is seen that in ovo feeding practices have improving effects on hatchery parameters and especially broiler feeding parameters, but more studies are needed in this regard.