The Dictionnaire philosophique (French: [dik.sjɔ.nɛʁ fi.lo.zɔ.fik]; lit. 'Philosophical Dictionary') is an encyclopedic dictionary published by the Enlightenment thinker Voltaire in 1764. The alphabetically arranged articles often criticize the Roman Catholic Church, Judaism, Islam, and other institutions. The first edition, released in June 1764, went by the name of Dictionnaire philosophique portatif. It was 344 pages and consisted of 73 articles. Later versions were expanded into two volumes consisting of 120 articles.

The first editions were published anonymously in Geneva by Gabriel Grasset. Due to the volatile content of the Dictionnaire, Voltaire chose Grasset over his usual publisher to ensure his own anonymity. There were many editions and reprints of the Dictionnaire during Voltaire's lifetime, but only four of them contained additions and modifications. Furthermore, another work published in 1770, Questions sur l'Encyclopédie, which contained reshaped and modified articles from the Encyclopédie always in alphabetical order, led many following editors to join this and the Dictionnaire (plus other minor works) in a unique opus. The Dictionnaire was a lifelong project for Voltaire. It represents the culmination of his views on Christianity, God, morality and other subjects.

The Enlightenment saw the creation of a new way of structuring information in books. The first work to employ this method was the Dictionnaire Historique et Critique (1697) by Pierre Bayle, in which the information is ordered alphabetically. Other important works using a similar structure followed, such as the Encyclopédie by Diderot and Jean d'Alembert. Having witnessed first-hand the popularity and many advantages of this form, Voltaire used this information while preparing the Philosophical Dictionary in 1752, although it was not completed until 1764.

Having had the opportunity to write his Dictionary at a later point in time, Voltaire saw that there were certain problems with previous dictionaries, chiefly that they were all lengthy, and thus very expensive and inaccessible for much of the population. Voltaire sought to create a text which would fit in one's pocket and be affordable because "revolutionary material must be small enough for people to carry with them". What he created is a text which educated and amused at the same time.

Voltaire's motivations for writing the Philosophical Dictionary can be seen as serendipitous. The idea was spawned at a dinner party in the court of Prince Frederick II of Prussia in 1752, during which he and other guests each agreed to write an article and share them the next morning. Voltaire consequently was the only guest to take the game seriously and the idea cascaded to form the Philosophical Dictionary.

The Philosophical Dictionary is structured in the tradition of Bayle, Diderot and d'Alembert – that is to say, alphabetically ordered. Although this order helps readers more easily find articles, this was not meant to be a dictionary or encyclopaedia in the same totalizing way of d'Alembert's project. Voltaire's writing is neither objective nor varied in opinion; the same arguments are made throughout the Philosophical Dictionary emphasizing the point of his discontent.

Many of the themes addressed by Voltaire in this book are addressed or touched upon in his work L'Infame. In this and other works, Voltaire is very concerned about the injustices of the Catholic Church, which he sees as intolerant and fanatical. At the same time, his work espouses deism (though he calls it theism, contrary to its modern meaning), tolerance and freedom of the press.

Because this work was written late in the author's life, coupled with the fact that it is compiled of articles written over an extended period of time, the work had many influences, which noticeably change, depending on the theme which the article addresses.