Barcodes are one of the most consequential inventions in the history of commerce and logistics. The concept was first patented in 1952 by Norman Joseph Woodland and Bernard Silver, who drew inspiration from Morse code by extending dots and dashes downward into thin and thick lines. However, it took over two decades for the technology to become practical. The first commercial barcode scan occurred on June 26, 1974, at a Marsh supermarket in Troy, Ohio, where a pack of Wrigley's Juicy Fruit chewing gum was scanned using a UPC barcode—a moment now commemorated in the Smithsonian Institution.

A barcode encodes data in the varying widths and spacings of parallel lines (bars). Each symbology—the technical term for a barcode format—defines its own rules for how characters map to bar patterns. CODE39, developed in 1974, uses nine elements (five bars and four spaces) per character, with three of the nine elements being wide, hence the name. It is self-checking, meaning a single printing defect typically will not cause a misread, which made it the standard for U.S. Department of Defense logistics (MIL-STD-1189) and remains widely used in automotive, government, and healthcare applications.

CODE128, introduced in 1981, is a much higher-density symbology that supports the full 128-character ASCII set. It achieves its compactness through three character sets (A, B, and C) that the encoder can switch between mid-barcode. Character Set C is particularly efficient for numeric data, encoding pairs of digits in a single symbol width. This makes CODE128 the preferred choice for shipping labels, package tracking, and any application where space is limited but the full alphanumeric character set is needed.

EAN-13 (European Article Number) and UPC-A (Universal Product Code) are the barcodes consumers encounter daily on retail products. UPC-A encodes a 12-digit number and was the original retail barcode standard in North America. EAN-13 extends this to 13 digits and is the global standard, with UPC-A being a subset (a UPC-A code is simply an EAN-13 with a leading zero). These barcodes include a check digit calculated using a modulo-10 algorithm, which catches most scanning errors. The number system is managed by GS1, a global standards organization that assigns manufacturer prefixes to ensure every product worldwide has a unique identifier.

The scanning process works by measuring the relative widths of bars and spaces as a laser or camera sweeps across the code. The scanner does not measure absolute widths; instead, it calculates ratios, which is why barcodes can be printed at various sizes and still scan correctly. Guard patterns at the beginning, middle, and end of the barcode help the scanner synchronize and determine the reading direction, allowing barcodes to be scanned in either orientation. Modern image-based scanners can even read damaged or poorly printed barcodes by analyzing the entire image rather than a single scan line.