ECE R129 certification, also known as i-Size, is the modern European standard for car seat approval. It classifies seats according to the height of the child, not the weight, and requires side impact tests. It also encourages prolonged rear-facing use and favours the ISOFIX system for attachment. The standard is divided into several phases (R129/01, R129/02, R129/03, R129/04) and gradually replaces the older ECE R44/04. It is considered the safest standard in the field of child transport.