Intermec introduced the first 2D code „Code 49“ in the year 1987. Since then, three major distinctive features for 2D codes have evolved.

Stacked codes are based on low height linear barcodes, which are stacked on top of each other. As a benefit of this code structure, specially adapted linear code scanners can read these codes.
The disadvantage of stacked codes is that they can only be identified with a very limited reading tilt. Presently, PDF417 defined by Symbol Technologies is the most popular stacked code type.

In general matrix codes are identified by a square representation of round, squared or other shaped data cells. For identification and segmentation purposes, matrix codes usually have an integrated „finder pattern“, which enables the decoders to distinguish the code from other markings of the coded objects. Typical finder patterns: Concentric rings, specially featured corner structures or predefined borders.
Most popular code symbologies are Data Matrix, QR-Code and Maxicode.

Various special compound code symbologies were created which consist of linear and matrix code segments. Both traditional linear code readers and new matrix code technology can be applied to continue with existing information structures.