Altruism (also called the ethic of altruism, moralistic altruism, and ethical altruism) is an ethical doctrine that holds that individuals have a moral obligation to help, serve, or benefit others, if necessary at the sacrifice of self interest. Auguste Comte's version of altruism calls for living for the sake of others. One who holds to either of these ethics is known as an "altruist."
The word "altruism" (French, altruisme, from autrui: "other people", derived from Latin alter: "other") was coined by Auguste Comte, the French founder of positivism, in order to describe the ethical doctrine he supported. He believed that individuals had a moral obligation to renounce self-interest and live for others. Comte says, in his Catéchisme Positiviste , that:
[The] social point of view cannot tolerate the notion of rights, for such notion rests on individualism. We are born under a load of obligations of every kind, to our predecessors, to our successors, to our contemporaries. After our birth these obligations increase or accumulate, for it is some time before we can return any service.... This ["to live for others"], the definitive formula of human morality, gives a direct sanction exclusively to our instincts of benevolence, the common source of happiness and duty. [Man must serve] Humanity, whose we are entirely."
The Catholic Encyclopedia says that for Comte's altruism, "The first principle of morality...is the regulative supremacy of social sympathy over the self-regarding instincts."  Author Gabriel Moran, (professor in the department of Humanities and the Social Sciences, New York University) says "The law and duty of life in altruism [for Comte] was summed up in the phrase : Live for others." 
Various philosophers define the doctrine in various ways, but all definitions generally revolve around a moral obligation to benefit others or the pronouncement of moral value in serving others rather than oneself. Philosopher C. D. Broad defines altruism as "the doctrine that each of us has a special obligation to benefit others."  Philosopher W. G. Maclagan defines it as "a duty to relieve the distress and promote the happiness of our fellows...Altruism is to...maintain quite simply that a man may and should discount altogether his own pleasure or happiness as such when he is deciding what course of action to pursue."  Some philosophers reject altruism, most notably Ayn Rand who advocated the moral philosophy of rational egoism.
Altruism is often seen as a form of consequentialism, as it indicates that an action is ethically right if it brings good consequences to others. James Fisher, in his article "Ethics" in the Internet Encyclopedia of Philosophy, states the altruist dictum as: "An action is morally right if the consequences of that action are more favorable than unfavorable to everyone except the agent." Altruism may be seen as similar to utilitarianism, however an essential difference is that the latter prescribes acts that maximize good consequences for all of society, while altruism prescribes maximizing good consequences for everyone except the actor.
Friedrich Nietzsche held that the idea that it is virtuous to treat others as more important than oneself is degrading and demeaning to the self. He also believed that the idea that others have a higher value than oneself hinders the individual's pursuit of self-development, excellence, and creativity. 
Ayn Rand held that one should pursue rational self-interest, and viewed altruism as an evil moral philosophy. She states that:
What is the moral code of altruism? The basic principle of altruism is that man has no right to exist for his own sake, that service to others is the only justification of his existence, and that self-sacrifice is his highest moral duty, virtue and value.
Do not confuse altruism with kindness, good will or respect for the rights of others. These are not primaries, but consequences, which, in fact, altruism makes impossible. The irreducible primary of altruism, the basic absolute, is self-sacrifice—which means: self-immolation, self-abnegation, self-denial, self-destruction—which means: the self as a standard of evil, the selfless as a standard of the good.
Do not hide behind such superficialities as whether you should or should not give a dime to a beggar. That is not the issue. The issue is whether you do or do not have the right to exist without giving him that dime. The issue is whether you must keep buying your life, dime by dime, from any beggar who might choose to approach you. The issue is whether the need of others is the first mortgage on your life and the moral purpose of your existence. The issue is whether man is to be regarded as a sacrificial animal. Any man of self-esteem will answer: "No." Altruism says: "Yes."
David Kelley, discussing Ayn Rand's views, says that "there is no rational ground for asserting that sacrificing yourself in order to serve others is morally superior to pursuing your own (long-term, rational) self-interest. Altruism ultimately depends on non-rational 'rationales,' on mysticism in some form..." Furthermore, he holds that there is a danger of the state enforcing that moral ideal: "If self-sacrifice is an ideal - if service to others is the highest, most honorable course of action - why not force people to act accordingly?" He believes this can ultimately result in the state forcing everyone into a collectivist political system. 
Norwegian eco-philosopher Arne Naess argues that environmental action based upon altruism — or service of the other — stems from a shrunken "egoic" concept of the self. Self-actualization will result, he argues, in the recovery of an "ecological self", in which actions formerly seen as altruistic are in reality a form of enlightened self-interest.
Finally, one argument is strictly logical. If person A acts in B's interests, and B acts in A's interests, who will be the final recipient of their generosity? While altruism can be seen as a virtue, it by itself cannot settle matters of fairness. An alternative to pure altruism is impartiality, exemplified by the ethic of reciprocity.