The presence of multiple limitations for bleeding time has led to the development of automated assays assessing primary hemostasis. Occlusion time measured on the Platel and Function Analyzer (PFA) is an innovative approach exploring primary hemostasis that has largely replaced bleeding time in the hospital setting due to its greater applicability. From a technical point of view, the test is equivalent in vitro to the traditional in vivo bleeding time which is also known as in vitro bleeding time. This book is a review of the literature on platelet occlusion time, with a detailed presentation of the PFA test and an update of the current knowledge on the use of this test in the dynamic exploration of primary hemostasis, as well as its interest in the biological monitoring of the therapeutic efficacy of anti-platelet agents (APA) and finally a comparison of this test with the classical tests exploring primary hemostasis.