In order to assess hemostasis for children, it is crucial to know the age-specific reference ranges of each coagulation test in the laboratory. Since reference ranges depend on reagents and analyzers, published reference ranges may not be always applicable to individual hospitals. There are a number of published age specific reference ranges; however, those reference ranges are quite variable and usually have a wide range. Also, gestational age affects newborns’ reference ranges. Therefore, it is suggested to establish own reference ranges of hemostasis tests in every laboratory if it has children’s patient population. However, it is challenging to collect specimens from “normal” infants, especially among newborns, since healthy babies do not come to hospital. In addition, the reference ranges need to be regularly verified or re-established whenever the reagents have a new lot. As a general rule, after 6 months of age, most hemostasis parameters reach adult levels with exception of protein C. With that being said, some patients may show delay of reaching the adult levels of the test. Ten clinical scenarios are presented in this chapter, which are the examples of developmental hemostasis that clinicians who manage children need to be aware of.