Rail freight is the backbone of a sustainable transport system, but innovations are necessary to increase its competitiveness. The Digital Automatic Coupler (DAC) is such a promising innovation to transform the rail freight sector. So far, harmonized definitions of its potential functionalities and use cases are missing in literature. This paper presents the DAC and the Full Digital Freight Train (FDFT) and gives an overview of its functionalities and potential benefits. First, the harmonized operational procedures for the future operation of the FDFT are presented. These provide the basis for potential applications of the DAC. Second, the future functions enabled by the DAC are outlined, categorized and evaluation criteria are discussed. The number of different use cases is large and illustrates the great potential of the DAC. However, challenges of complex technical development and decision-making processes are accordingly large. To tackle these, the current DAC development takes place within the Europe’s Rail project Transforming Europe’s Rail Freight (TRANS4M-R) which will also be introduced. This overview provides a starting point for further standardization of processes and definitions.