International standard defining the formats for printed matter, used in particular in European countries (see page 72). ISO 216 formats are divided into Series A and Series B and indicate finished formats of printed matter, in particular for correspondence. Series C, defined by the ISO 269 standard, refers the sizes of envelopes intended to contain Series A and Series B formats. The bestknown formats are A4 and A3. These formats are often known as DIN, after Deutsches Institut für Normung (German Standards Institute), that defined these measurements for the first time in 1922.