Peter Singer is one of the most outstanding contemporary philosophers of our time. Like John Rawls, who preached egalitarian liberalism, Singer has identified moral and ethical issues that are central to a just society and the good life.
Singer grapples with issues such as how best to live — who should live and who should die, the relative importance of humans and other animals, including humans of limited abilities, and the obligations we have to people we have never met, especially the millions of desperately poor people in the third world .
Singer's moral theories prove to be timely in modern day political and ethical discourse. For instance, Singer has endorsed medical discrimination against the elderly in the Covid crises.
By doing this, Singer is taking a moral approach similar approach to John Stewart Mills theory of Utilitarianism. Singer and Mill both agree on the idea of selflessness, which is the idea that we can end human suffering by prioritizing the needs of society over any one individual.
Singer's writings and ideas provide societies with the tools to solve ethical quandaries in the world — such as the problem of pain and suffering, which is experienced by all living beings capable of suffering, and this is often due to world poverty. Singer's prescient theories and suggestions for solving economic and moral issues are not without controversy.
Singer preaches in favor of the ethical virtues of contentious issues such as euthanasia, the deliberate killing — sometimes called 'mercy killings' — of some human beings to liberating animals mistreated and killed for diverse reasons. Singer's immense prescience continues when he contends that we in the so called affluent world have a moral obligation to donate the majority of our income to help the poverty stricken millions in less-developed countries.
This idea has found few advocates, even though few people fail to identify the flaws in moral reasoning. Indeed, in countries like the U.S, many citizens are even reluctant to pay taxes to fellow citizens that are less lucky than them. By contrast, Singer has vehemently persuaded people to boycott factory farming — and he has had some success.
If Singer's writings could be attributed to one main idea, it would be that he is highly concerned with the problem of suffering. Although many scholars share Singer's concern about suffering, many of them disagree with him on the methods and terms he proposes that would minimize human suffering.
The controversial areas of Singer's work grapple with issues such as: whether or not we have an obligation to reduce the disparity between the rich and poor, whether human life is sacred, and whether we should radically transform our way of life to avoid the mistreatment of animals.
More crucial thought experiments and ethical quandaries that Singer engages in include: should we, for example, allow the killing, at the request of their parents, of newborn babies, up to a month of age, who have severe birth deficits that they are incapable of experiencing life in ways that we normally identify as human? Are they not yet persons? Why or why not?
Singer ponders more ethical quandaries in his book Practical Ethics, which covers a wide array of topics. In this book, Singer unpacks ethical quandaries that confront us daily, such as: is it right to spend money on entertaining ourselves when we could be could use it to help people living in extreme poverty? Are we justified in treating animals as nothing more than machines producing flesh for us to eat? 
Should we drive a car — thus emitting greenhouse gases that warm the planet — if we could walk, cycle or use public transport? These are prescient questions that if answered correctly, they would create a more ethical and sustainable future for the next generation.
Singer makes important observation in the book that help clear up confusion about the role of ethics in building the just and ideal society. For instance, Singer dispels the notion that ethics is only an ideal system that cannot be effectively put into practice. Singer proposes that an ethical judgement that is no good in practice must suffer from a theoretical defect as well, for the whole point of ethical judgment is to guide practice.
Singer claims that ethics is not based in religion, and is in fact entirely independent from religion. From this perspective, Singer is crafting a new understanding of the origins of morality, which in his view, should only function to free us from two putative masters, God and nature. Singer emphasizes that although we have inherited a set of moral institutions from our ancestors, we must update them and work out which of them should be changed.
Singer rightfully undermines cultural relativists bu using the following thought experiment: If 'slavery is wrong' means 'my society disapproves of slavery', the someone who lives in a society that does not disapprove of slavery is, in claiming that slavery is wrong, making a simple factual error.
Singer also highlights the fact that ethics is not merely a matter of subjective taste or opinion. In fact, Singer views ethics as an entirely objective phenomena. From this perspective, Singer is saying:
"If those who say that ethics is subjective mean by this that when I say that cruelty to animals is wrong I am really only saying that I disapprove of cruelty to animals, they are faced with an aggravated form of one of the difficulties of relativism: the inability to account for ethical disagreement."
"What was true for the relativist in the case of disagreement between people from different societies is for the subjectivity true of all ethical disagreement. I say cruelty to animals is wrong; you say it is not wrong. If this means that I disapprove of cruelty to animals and you do not, both statements may be truth and there is nothing to argue about."
Singer provides a nuanced ethical approach that address multifaceted ethical quandaries. Singer takes positions that are bound to maximize human flourishing and minimize human suffering on our planet. For instance, Singer promotes ethical vegetarianism and viable solutions to world poverty.
 Singer, Peter. Peter Singer under fire: the moral iconoclast faces his critics. Vol. 3. Open Court Publishing, 2009.
 Singer, Peter. Practical ethics. Cambridge University Press, 2011.