The Pensées (literally, "thoughts") represented an apology for the Christian religion by Blaise Pascal, the renowned 17th century philosopher and mathematician. Pascal's own religious conversion had led him into a life of asceticism, and the Pensées were in many ways his life's work.

Although they appear to consist of ideas and jottings, some of which are incomplete, it is now believed that Pascal had, prior to his untimely death in 1662, already planned out the order of the book and had arranged the individual scraps of paper, on which the "thoughts" were written, accordingly. Those responsible for his effects, failing to recognise the basic structure of the work, handed them over to be edited, and they were published in 1669. It was not until the beginning of the 20th century that scholars understood Pascal's intention, and present-day editions of the book contain his "thoughts" in more or less the order he left them.

The original layout of the individual notes was in fact recorded in situ, although this was not reflected until recently in editions of the work. The structure of the apology is best described by H.F. Stewart D.D. in the preface to his translation of the Pensees: Part I shows "from Nature" that man is wretched without God, Part II shows "from Scripture" that Jesus is the Redeemer of mankind. Part I subdivides into Ia (man without God) and Ib (man with God) to show man's inherent wretchedness. The themes of Part I are largely in the tone of vanitas mundi, after the tradition of Solomon's book of Ecclesiastes, while the many short maxims inserted into the text are reminiscent of Solomon's Book of Proverbs.

The best-known quotations from the Pensées include:

Le coeur a ses raisons, que la raison ne connait point.

("The heart has its reasons, of which reason knows nothing")

Le silence éternel de ces espaces infinis m'effraie.

("The eternal silence of these infinite spaces terrifies me.")

L'homme n'est qu'un roseau, le plus faible de la nature, mais c'est un roseau pensant.

("Man is only a reed, the weakest thing in nature, but he is a thinking reed.")