A Christogram (Latin: Monogramma Christi) is a monogram or combination of letters that forms an abbreviation for the name of Jesus Christ, traditionally used as a religious symbol within the Christian Church.

One of the oldest Christograms is the Chi-Rho (☧). It consists of the superimposed Greek letters chi (Χ) and rho (Ρ), which are the first two letters of the Greek χριστός, 'Christ'. It was displayed on the labarum military standard used by Constantine I in 312 AD. The IX monogram () is a similar form, using the initials of the name Ἰησοῦς (ὁ) Χριστός, 'Jesus (the) Christ', as is the ΙΗ monogram (), using the first two letters of the name ΙΗΣΟΥΣ, 'JESUS' in uppercase.

There were a very considerable number of variants of "Christograms" or monograms of Christ in use during the medieval period, with the boundary between specific monograms and mere scribal abbreviations somewhat fluid.

The name Jesus, spelled ΙΗΣΟΥΣ in Greek capitals, has the abbreviations IHS (also written JHS, IHC, or ΙΗΣ). The name Christus , spelt ΧΡΙΣΤΟΣ, has XP (and inflectional variants such as IX, XPO, XPS, XPI, XPM). In Eastern Christian tradition, the monogram ΙϹΧϹ (with Overline indicating scribal abbreviation) is used for Ἰησοῦς Χριστός in both Greek and Cyrillic tradition.

A Middle Latin term for abbreviations of the name of Christ is chrisimus. Similarly, the Middle Latin crismon, chrismon refers to the Chi-Rho monogram specifically.

In antiquity, the cross, i.e. the instrument of Christ's crucifixion (crux, stauros), was taken to be T-shaped, while the X-shape ("chiasmus") had different connotations. There has been scholarly speculation on the development of the Christian cross, the letter Chi used to abbreviate the name of Christ, and the various pre-Christian symbolism associated with the chiasmus interpreted in terms of "the mystery of the pre-existent Christ".

In Plato's Timaeus, it is explained that the two bands which form the "world soul" (anima mundi) cross each other like the letter Chi, possibly referring to the ecliptic crossing the celestial equator:

And thus the whole mixture out of which he cut these portions was all exhausted by him. This entire compound divided lengthways into two parts, which he joined to one another at the centre like the letter X, and bent them into a circular form, connecting them with themselves and each other at the point opposite to their original meeting-point; and, comprehending them in a uniform revolution upon the same axis, he made the one the outer and the other the inner circle.