Year 1623 (MDCXXIII) was a common year starting on Sunday (link will display the full calendar) of the Gregorian calendar and a common year starting on Wednesday of the 10-day slower Julian calendar.

Blaise Pascal (French pronunciation: [blɛz paskal]; 19 June 1623 – 19 August 1662), was a French mathematician, physicist, inventor, writer and Catholic philosopher. He was a child prodigy who was educated by his father, a tax collector in Rouen. Pascal's earliest work was in the natural and applied sciences where he made important contributions to the study of fluids, and clarified the concepts of pressure and vacuum by generalizing the work of Evangelista Torricelli. Pascal also wrote in defense of the scientific method.

In 1642, while still a teenager, he started some pioneering work on calculating machines, and after three years of effort and 50 prototypes he invented the mechanical calculator. He built twenty of these machines (called the Pascaline) in the following ten years. Pascal was an important mathematician, helping create two major new areas of research: he wrote a significant treatise on the subject of projective geometry at the age of sixteen, and later corresponded with Pierre de Fermat on probability theory, strongly influencing the development of modern economics and social science. Following Galileo and Torricelli, in 1646 he refuted Aristotle's followers who insisted that nature abhors a vacuum. Pascal's results caused many disputes before being accepted.

William Byrd (1540 or late 1539 – 4 July 1623) was an English composer of the Renaissance. He wrote in many of the forms current in England at the time, including various types of sacred and secular polyphony, keyboard (the so-called Virginalist school) and consort music.

Knowledge of Byrd's biography expanded in the late 20th century, thanks largely to the research of John Harley (Harley, 1997). Following the discovery of a document dated 2 October 1598 in which Byrd's age is given as "58 years or there abouts," it now appears that he was born in 1540. The older dating 1542–3 is derived from Byrd's will (endorsed on 22 November 1622) which describes him as 'in the 80th year of my age'. It now becomes clear that it must have been drafted about three years earlier than the date of endorsement. Byrd was born in London, the son of a Thomas Byrd (not Thomas Byrd of the Chapel Royal) about whom little is known. Byrd had two brothers, Symon'd and John, and four sisters. It is clear from a reference in the prefatory material in the Tallis/Byrd Cantiones of 1575 that Byrd was a pupil of Thomas Tallis, then the leading composing member of the Chapel Royal Choir. Byrd also worked in collaboration with two other Chapel Royal singing-men, John Sheppard and William Mundy, on one of his earliest compositions, a contribution to a joint setting of the alternatim psalm In exitu Israel composed for the procession to the font at the Paschal Vigil. As an item for the Sarum liturgy this was presumably composed near the end of the reign of Mary Tudor (1553–1558), whose Catholic beliefs impelled her to revive Sarum liturgical practices during her brief reign. In view of these contacts it is reasonable to speculate that Byrd was a Chapel Royal choirboy, though the surviving records do not name the choristers individually.