Tally marks, or hash marks, are a unary numeral system. They are a form of numeral used for counting. They allow updating written intermediate results without erasing or discarding anything written down. However, because of the length of large numbers, tallies are not commonly used for static text.

In Europe and North America, tally marks are most commonly written as groups of five lines. The first four lines are vertical, and every fifth line runs diagonally or horizontally across the previous four vertical lines, from the top of the first line, to the bottom of the fourth line (the popular direction may vary from region to region). The resulting mark is known as a five-bar gate, from its similarity to the same. In some variants, the tenth tally is indicated by an X through the previous four rather than just a line, and in still other variants, the diagonal/horizontal slash is used on its own when five or more units are added at once. Two groups of five lines (i.e. ten tally marks) are sometimes circled.

For the Jamaican work song, see Day-O (The Banana Boat Song). For the Batman villain who carves tally marks into his body to mark his murders, see Victor Zsasz.

The Tally Man is the name of two fictional characters in the DC Universe. Both characters are supervillains.

The few glimpses provided into the Tally Man's past reveal a tragic childhood. Starving and living in rags, the boy who was to become the Tally Man lived with his mother and sister, in constant fear of the criminals who threatened the family for the money his father had borrowed from them years before. After his father died, those same criminals extorted his weekly fee from the deceased man's wife. The boy begged his mother not to pay, but she tearfully replied, "Everybody has to pay the tally man." One night, when the collector came, his mother could not afford to pay and the criminal beat her. Filled with rage, the boy attacked and brutally killed the money collector with a fireplace poker. The 12-year-old boy was arrested for murder, and abused horribly by the others in the boy's prison, who called him a "mama's boy." After his release, the boy returned home. When he discovered his sister had died of starvation and his mother had committed suicide, his mind snapped.