QR Code is a matrix barcode whose main features are large storage capacity, fast decoding and correcting errors. It consists of black and white modules which together form patterns. There are several types of patterns that are necessary for the code to work properly and are called „functioning patterns“. The rest of them make up the encoding region. In addition to the structure, this thesis describes the processes of coding and decoding, as well as the differences in capacities between different versions. Besides classic QR, there are many variations of it that vary in appearance, features and applications. Moreover, despite having large storage capacity, there are many ways for its further increasing. This thesis describes some of the most common types of modes based on the principle of using multiple colors or compressing data before coding in QR. Many other two-dimensional codes exist today, and this paper briefly lists some of them whose appearance is similar to QR, such as PDF417, MaxiCode and DataMatrix code. The thesis concludes with their comparison to the QR code.