This chapter focuses on responsibility of States and international organisations under international law. Initial sections draw distinction between responsibility and liability, and clarify the concept of abuse of rights. Then a complex issue of attribution of internationally wrongful acts to States is discussed in its wide variety and in diverse situations. Responsibility of States also involves the discussion of defences, reparation, and countermeasures (otherwise also known as reprisals) that are undertaken by States to enforce their own rights when those are violated by another State. The final section focuses on the responsibility of international organisations.