Meditations on First Philosophy: In Which the Existence of God and the Immortality of the Soul Are Demonstrated

Meditations on First Philosophy is a philosophical treatise by René Descartes first published in Latin. The original Latin title is Meditationes de prima philosophia, in qua Dei existentia et animæ immortalitas demonstratur.

The book is made up of six meditations, in which Descartes first discards all belief in things which are not absolutely certain, and then tries to establish what can be known for sure. The meditations were written as if he were meditating for 6 days: each meditation refers to the last one as "yesterday".

The Meditations consist of the presentation of Descartes' metaphysical system in its most detailed level and in the expanding of Descartes' philosophical system, which he first introduced in the fourth part of his Discourse on Method. Descartes' metaphysical thought is also found in the Principles of Philosophy, which the author intended to be a philosophy guidebook.