Millions of people in the world are affected by extreme poverty. Most of the citizens of the affluent western countries recognise that they have an obligation not to do harm to other people, no matter who they are, or whatever country they happen to live in. In addition, many people have a strong intuition that something should be done to help the people who are suffering in other countries, and that it would be just that everyone would have an adequate standard of living. The aim of this Master's thesis is to examine how the claim that justice should be realised on a global level could be justified. To do this, I will assess the arguments of Peter Singer, John Rawls, and Henry Shue, who base their theories on utilitarianism, contractarianism, and human rights respectively. Singer's argument is expressed in his article 'Famine, Affluence, and Morality' (1972). The basis of John Rawls's theory can be found in his A Theory of Justice (1971), and his later arguments concerning global justice in Law of Peoples (1999). However, expanding Rawls's theory on a global level is done by Charles Beitz and Thomas Pogge, whose arguments have been expressed in a selection of publications. Henry Shue elaborates his theory in his Basic Rights: Subsistence, Affluence, and U.S. Foreign Policy (1980). Even though these philosopher's have very different theoretical backgrounds and justifications for their arguments, their perspectives share the idea of universal humanity and equality between human beings. Thus it will become evident that the same outcome can be reached by very different routes. I will examine the theories, pick up their strong points and weaknesses, and evaluate whether their normative prescriptions could be realistically implemented. The aim is also to try to make the issue of global justice more understandable, clarify the important points, outline the framework of the discussion, and compare the different views taken on the subject. It will become clear that the theories are insufficient to give a justification for the question on global justice, as they face some insurmountable problems both on theoretical and practical level. Their incommensurability also makes it difficult to make comparisons to find out, which of them could be more useful or realisable. However, the theories have an important function, as they provide the framework, without which the conversation on the subject would be difficult, maybe even impossible. At the end of the thesis it will be suggested that perhaps the issue of global justice should be approached from a totally new perspective. The orthodox ways of thinking that have been taken for granted should thus be challenged. Whatever the case, the question and problems of global justice cannot be swept under the carpet, as they are something that become more urgent by day, effecting all human beings.