Sepsis occurs when an infection, caused by bacteria, a virus, or a fungus, enters the body and throws the immune system out of balance. Instead of protecting the body, the immune response may become too strong and start damaging healthy organs, or it may become too weak and fail to control the infection. Both situations can be life-threatening. Even people who survive sepsis may experience long-term health problems, such as new infections, heart and blood vessel diseases, or early death. This study aims to better understand how the immune system behaves during and after sepsis. We believe that there are different types of immune responses in sepsis, called immunotypes. We will identify these immunotypes by examining substances in the blood and changes in immune cells. We will then study which immunotypes help protect patients and which may cause short- or long-term harm. Understanding these immunotypes may make it possible in the future to quickly determine what type of immune response a patient with sepsis has. This could help doctors choose the best treatment for each individual patient. A total of 400 patients with sepsis from the intensive care unit will take part in this study. We will collect blood samples at several time points and gather information about their health. Participants will be followed from their intensive care admission until one year after they return home.