Spinoza's thinking is summarised in his Ethics is one of the most significant books in the history of philosophy. Written in Latin between 1661/2 and 1675–but not, significantly, published until 1677, following its author’s death–the work owes its title to the fact that it addresses questions of right and wrong human action. Yet this title is misleading, as Ethics is also a book about God and the world, an examination of the structure of the mind and its relation to the body, a detailed account of the psychology of emotions, and an attempt to understand human action. Ethics’ rejection of free will and exploration of the consequences of determinism—the philosophical view that all human action is determined by causes outside of free will—remains radical to this day. The book argues that altruism is a consequence of, rather than being contradictory to, the pursuit of self-interest. Its insightful analysis of human emotions concludes with an account of the good life as one characterised by joy and the power for action. The work is demanding for the reader, but is clearly a key text of modern philosophy.

The questions that Ethics addresses, including what the universe is, how we know it, how our emotions relate to it, and how we should act within it, were as important then as they are today, and it is to the lasting credit of Ethics that it addresses them in such a systematic and original way. Even the work’s geometric style is not accidental; it reflects the author’s belief in universal laws that govern everything equally and without preference or gaps. But by thinking out and writing down such views, Spinoza was placing himself in opposition to a lot of what was then mainstream and accepted thought.

To put all this in context: Spinoza was born in Amsterdam, Holland, in 1632 and given the Hebrew name Baruch. Raised among that city’s Marrano community, he worked for a period in his family’s importing business, while at the same time showing promise as a scholar. Little is known about Spinoza during those early years, which seem to have involved a degree of controversy—most likely due to his unorthodox theological views.

Spinoza's views were considered dangerous for several reasons. For one thing, they embodied a serious critique of all organised religion, and in particular argued against the use of religion to buttress political power. Spinoza also argued against the idea that God had a "purpose" for man and in favour of political libertalism and religious tolerance. He appears to have been a supporter of the controversial Jan de Witt, head of the Dutch government in the 1670s, and much of his work can be read as a defence of de Witt's political project.

Such unorthodoxy was probably the reason why Spinoza was subjected to a knife attack in 1656. On July 27 of that same year he was excommunicated from his community in a writ of cherem, the Hebrew term for expulsion of a member of the community. This followed accusations against him of “horrible heresies” and “monstrous actions.” The reasons remain unclear, but are likely to stem from his unorthodox views on prophecy, immortality, and God. Those who had lived, worked, and studied alongside him were then forbidden to associate with him. In 1661, Spinoza left Amsterdam for the village of Rijnsburg, near Leiden, in Holland, where he began work on Ethics. At the same time, he Latinized his name to Benedictus, probably indicating his sympathy for the principles of humanism, a movement disliked and sometimes feared by religious leaders at this time. In Rijnsburg, as well as across later moves to Voorburg and the Hague, Spinoza supported himself in his philosophical work by grinding lenses for optical instruments.

In exile, Spinoza corresponded with a network of friends and supporters who built his reputation and circulated early drafts of Ethics, at least across Holland and England. This group, many of whom were Mennonites, members of non-conformist Protestant sects, attracted the suspicion of the Netherlands' political and religious authorities. Those authorities grew increasingly hostile toward certain intellectual circles—if not wider culture—during the seventeenth century in Europe, particularly in England and the Netherlands. His friends encouraged him to publish Ethics, but Spinoza hesitated, discouraged by his excommunication and the hostile reaction to another work, his Tractatus Thelogico-Politicus ("Theological-Political Treatise"), published anonymously in 1670 and containing many similar ideas to those in Ethics.

Spinoza’s caution would soon prove justified, as the fate of his work ended up being tied to that of de Witt’s leadership. In 1672 (known in Dutch as the Rampjaar or Disaster-year), as a result of the Franco-Dutch War, de Witt and his followers were overthrown and lynched by royalists. Spinoza’s anonymity was lost, and in this climate his work soon came under attack as being “forged in Hell by a renegade Jew and the Devil, and issued with the knowledge of Jan de Witt.” This led to it being condemned and banned by the Dutch Reformed Church in 1674. Ethics, published after Spinoza’s death, would come to be attacked in a similar way during the following century. This was a time when being described as a follower of Spinoza would amount to a kind of insult among philosophers. It was only around the late eighteenth century, and not without a measure of hesitation, that it became permissible to include Spinoza’s work as part of serious philosophical debate.