Baruch or Benedict de Spinoza (Hebrew: ברוך שפינוזה‎, Portuguese: Bento de Espinosa, Latin: Benedictus de Spinoza) (November 24, 1632 – February 21, 1677) was a Dutch philosopher of Portuguese Jewish origin. Revealing considerable scientific aptitude, the breadth and importance of Spinoza's work was not fully realized until years after his death. Today, he is considered one of the great rationalists of 17th-century philosophy, laying the groundwork for the 18th century Enlightenment and modern biblical criticism. By virtue of his magnum opus, the posthumous Ethics, in which he opposed Descartes' mind–body dualism, Spinoza is considered to be one of Western philosophy's most important philosophers. Philosopher and historian Georg Wilhelm Friedrich Hegel said of all modern philosophers, "You are either a Spinozist or not a philosopher at all."

Though Spinoza was active in the Dutch Jewish community and extremely well-versed in Jewish texts, his controversial ideas eventually led community leaders to issue a cherem (Hebrew: חרם, a kind of excommunication) against him, effectively dismissing him from Jewish society at age 23. Some historians argue that the Roman Catholic Church forced them to do so. Other historians, notably Richard Popkin, question the historical veracity of the documents claiming Spinoza was issued a cherem, which emerged close to 300 years after Spinoza's death. Likewise, all of Spinoza's works were listed on the Index Librorum Prohibitorum (List of Prohibited Books) by the Roman Catholic Church. Spinoza lived quietly as a lens grinder, turning down rewards and honors throughout his life, including prestigious teaching positions, and gave his family inheritance to his sister. Spinoza's moral character and philosophical accomplishments prompted 20th century philosopher Gilles Deleuze to name him "the 'prince' of philosophers." Spinoza died at the age of 44 of a lung illness, perhaps tuberculosis or silicosis exacerbated by fine glass dust inhaled while plying his trade. Spinoza is buried in the churchyard of the Nieuwe Kerk on Spui in The Hague.

Spinoza's ancestors were of Sephardic Jewish descent, and were a part of the community of Portuguese Jews that grew in the city of Amsterdam after the Alhambra Decree in Spain (1492) and the Portuguese Inquisition (1536) had led to forced conversions and expulsions from the Iberian peninsula. Some historians argue the Spinoza family ("Espinosa" in Portuguese) had its origins in Espinosa de los Monteros, near Burgos, Spain. Others claim they were Portuguese Jews who had moved to Spain and then returned to their home country in 1492, only to be forcibly converted to Catholicism in 1498. Spinoza's father was born roughly a century after this forced conversion in the small Portuguese city of Vidigueira, near Beja in Alentejo. When Spinoza's father was still a child, Spinoza's grandfather, Isaac de Spinoza (who was from Lisbon), took his family to Nantes in France. They were expelled in 1615 and moved to Rotterdam, where Isaac died in 1627. Spinoza's father, Miguel, and his uncle, Manuel, then moved to Amsterdam where they reassumed their Judaism. Manuel changed his name to Abraão de Spinoza, though his "commercial" name was still the same.

Baruch Spinoza was born in Amsterdam, in the Netherlands. His mother Ana Débora, Miguel's second wife, died when Baruch was only six years old. Miguel was a successful importer/merchant and Baruch had a traditional Jewish upbringing; however, his critical, curious nature would soon come into conflict with the Jewish community. Wars with England and France took the life of his father and decimated his family's fortune but he was eventually able to relinquish responsibility for the business and its debts to his brother, Gabriel, and devote himself to philosophy and optics.

Spinoza became known in the Jewish community for positions contrary to prevailing Jewish belief of the period, wherein he harbored critical positions towards the anti-maimonidean dominance of Jewish religious texts that persisted since the Maimonidean Controversy. On 27 July 1656, the Jewish community issued to him the writ of cherem (Hebrew: חרם, a kind of excommunication). Righteous indignation on the part of the synagogue elders at Spinoza's heresies was not the sole cause for the excommunication; there was also the practical concern that his ideas, which disagree equally well with the orthodoxies of other religions as with Judaism, would not sit well with the Christian leaders of Amsterdam and would reflect badly on the whole Jewish community, endangering the limited freedoms that the Jews had achieved in that city. The terms of his cherem were severe. He was, in Bertrand Russell's words, "cursed with all the curses in Deuteronomy and with the curse that Elisha pronounced on the children who, in consequence, were torn to pieces by the she-bears." The cherem was, atypically, never revoked. Following his excommunication, he adopted the first name Benedictus, the Latin equivalent of his given name, Baruch; they both mean "blessed". In his native Amsterdam he was also known as Bento (Portuguese for Benedict or blessed) de Spinoza, which was the informal form of his name. The ban, written in Portuguese, is still preserved in the archives of the Amsterdam community. The pronouncement preceding the ban reads:

The chiefs of the council make known to you that having long known of evil opinions and acts of Baruch de Spinoza, they have endeavored by various means and promises to turn him from evil ways. Not being able to find any remedy, but on the contrary receiving every day more information about the abominable heresies practiced and taught by him, and about the monstrous acts committed by him, having this from many trustworthy witnesses who have deposed and borne witness on all this in the presence of said Spinoza, who has been convicted; all this having been examined in the presence of the Rabbis, the council decided, with the advice of the Rabbi, that the said Spinoza should be excommunicated and cut off from the Nation of Israel.

It has often been noted that, in view of Christian opposition to Spinoza's opinions, the Jewish community had little option but to dissociate itself from Spinoza's "heresies." After his cherem, it is reported that Spinoza lived and worked in the school of Franciscus van den Enden, who taught him Latin in his youth and may have introduced him to modern philosophy, although Spinoza never mentions Van den Enden anywhere in his books or letters. Van den Enden was a Cartesian and atheist who was forbidden by the city government to propagate his doctrines publicly.

During this period Spinoza also became acquainted with several Collegiants, members of an eclectic sect with tendencies towards rationalism. Many of his friends belonged to dissident Christian groups which met regularly as discussion groups and which typically rejected the authority of established churches as well as traditional dogmas. Textbooks and encyclopedias often depict Spinoza as a solitary soul who eked out a living as a lens grinder; in reality, he had many friends but kept his needs to a minimum. One reviewer noted "No one has ever come nearer to the ideal life of the philosopher than Spinoza." Another wrote: "As a teacher of reality, he practiced his own wisdom, and was surely one of the most exemplary human beings ever to have lived." "In outward appearance he was unpretending, but not careless. His way of living was exceedingly modest and retired; often he did not leave his room for many days together. He was likewise almost incredibly frugal; his expenses sometimes amounted only to a few pence a day." "He appears to have had no sexual life." Spinoza also corresponded with Peter Serrarius, a radical Protestant and millennarian merchant. Serrarius is believed to have been a patron of Spinoza at some point. By the beginning of the 1660s, Spinoza's name became more widely known, and eventually Gottfried Leibniz and Henry Oldenburg paid him visits, as stated in Matthew Stewart's The Courtier and the Heretic. Spinoza corresponded with Oldenburg for the rest of his short life.

The writings of Rene Descartes have been described as "Spinoza's starting point." Spinoza's first publication was his geometric exposition (formal math proofs) of Descartes, Parts I and II of Descartes' Principles of Philosophy (1663). Spinoza has been associated with Leibniz and Descartes as "rationalists" in contrast to "empiricists". From December 1664 to June 1665, Spinoza engaged in correspondence with Blyenbergh, an amateur Calvinist theologian, who questioned Spinoza on the definition of evil. Later in 1665, Spinoza notified Oldenburg that he had started to work on a new book, the Theologico-Political Treatise, published in 1670. Leibniz disagreed harshly with Spinoza in Leibniz's own published Refutation of Spinoza, but he is also known to have met with Spinoza on at least one occasion (as mentioned above), and his own work bears some striking resemblances to specific important parts of Spinoza's philosophy (Monadology).

When the public reactions to the anonymously published Theologico-Political Treatise were extremely unfavourable to his brand of Cartesianism, Spinoza was compelled to abstain from publishing more of his works. Wary and independent, he wore a signet ring engraved with his initials, a rose, and the word "caute" (Latin for "cautiously"). The Ethics and all other works, apart from the Descartes' Principles of Philosophy and the Theologico-Political Treatise, were published after his death, in the Opera Posthuma edited by his friends in secrecy to avoid confiscation and destruction of manuscripts. The Ethics contains many still-unresolved obscurities and is written with a forbidding mathematical structure modeled on Euclid's geometry and has been described as a "superbly cryptic masterwork."

Spinoza spent his remaining 21 years writing and studying as a private scholar. He preached a philosophy of tolerance and benevolence and was described as living "a saintly life." Spinoza relocated from Amsterdam to Rijnsburg (near Leiden) around 1661 and later lived in Voorburg and The Hague respectively. He earned a comfortable living from lens-grinding. While the lens-grinding aspect of Spinoza's work is uncontested, the type of lenses he made is in question. Many have said he produced excellent magnifying glasses, and some historians credit him with being an optician (in the sense of making lenses for eyeglasses). He was also supported by small, but regular, donations from close friends.

He died in 1677 while still working on a political thesis. His premature death was due to lung illness, possibly the result of breathing in glass dust from the lenses he ground. Or also possibly due to a syndrome, known as Familial Mediterranean Fever (FMF) which is a hereditary inflammatory disorder that affects groups of people originating from around the Mediterranean Sea (hence its name). It is prominently present in the Armenian people, Sephardi Jews (and, to a much lesser extent, Ashkenazi Jews), people from Turkey, and the Arab countries. Later, a shrine was made of his home in The Hague.

Only a year earlier, Spinoza had met with Leibniz at The Hague for a discussion of his principal philosophical work, Ethics, which had been completed in 1676. This meeting was described in Matthew Stewart's The Courtier and the Heretic. Spinoza never married, nor did he father any children. When he died, he was considered a heathen anti-religionist by the general population, and when Boerhaave wrote his dissertation in 1688 he attacked the doctrines of Spinoza. He claimed later that defense of Spinoza's lifestyle cost him his reputation in Leiden and a post as minister.

Amsterdam and Rotterdam were important cosmopolitan centers where merchant ships from many parts of the world brought people of various customs and beliefs. It was this hustle and bustle which ensured, as in the Mediterranean region during the Renaissance, some possibility of free thought and shelter from the crushing hand of ecclesiastical authority. Thus, Spinoza no doubt had access to a circle of friends who were basically heretics in the eyes of tradition. One of the people he must have known was Niels Stensen, a brilliant Danish student in Leiden; others were Coenraad van Beuningen and his cousin Albert Burgh, with whom Spinoza is known to have corresponded.