The main objective of our chapter is to present a group-level theory of helping and altruism within and across group boundaries and to review the empirical evidence in support of its key assumptions. We derive the basic tenets of this theory from the integration of two social psychological research traditions: research and theory on group processes and intergroup relations and research into helping behaviour and altruism. A key proposition of the theoretical account presented in our chapter is that salient ingroup/outgroup distinctions play a crucial role in moderating the motivational processes underlying helping owing to their effects on self–other similarities. In a first part, we elaborate on the specific predictions concerning motivational differences in ingroup and outgroup helping. It also outlines the subtle ingroup/outgroup biases in helping that might result from these motivational differences. Moreover, we propose different factors (in the sense of interventions) that can reduce ingroup/outgroup biases in helping. In a second part of the chapter, we present empirical data from a research programme designed to test these propositions. Here, we refer to a coordinated series of studies employing a variety of research methodologies (field research, laboratory experiments) and focusing on different intergroup contexts (natural groups, artificial groups), different samples of research participants (community volunteers and students, Westerners and Muslims, helpers and recipients of help), and different forms of helping situations (volunteering versus spontaneous helping). In a final part, we (re-)address the issue of outgroup discrimination in helping, taking a closer look at the subtleties of this phenomenon and its consequences for potential recipients of help.