The effective altruism movement consists of a growing global community of people who organise significant parts of their lives around the two key concepts, represented in its name. Altruism is the idea that if we use a significant portion of the resources in our possession-whether money, time, or talents-with a view to helping others then we can improve the world considerably. When we do put such resources to altruistic use, it is crucial to focus on how much good this or that intervention is reasonably expected to do per unit of resource expended (as a gage of effectiveness). Global poverty is a widely-used case study in introducing and motivating effective altruism, but if the ultimate aim is to do the most good one can with the resources expended then it is far from obvious that global poverty alleviation is highest priority cause area. In addition to ranking possible poverty-alleviation interventions against one another, we can also try to rank interventions aimed at very different types of outcome against one another. This includes, for example, efforts focused on animal welfare or future generations. The scale and organisation of the effective altruism movement encourage careful dialogue on questions that have perhaps long been there, throwing them into new and sharper relief, and giving rise to previously unnoticed questions. In the first volume of its kind, a group of internationally recognised philosophers, economists, and political theorists present refined and in-depth explorations of issues that arise once one takes seriously the twin ideas of altruistic commitment and effectiveness.