For this question, it is important to notice that the development of digital learning materials and their usage is active and continuous in practice, but there may not be much research about it, and the research may not be up to date. In this answer, we will not examine, in particular, the efficiency of the usage, simply because the “efficiency” of learning can be understood in so many ways (see also the question “What is good learning?”). Efficiency can only be measured in relation to goals, and these are determined by the pedagogy used in a certain learning situation or educational settings; this approach sets up requirements for the adequate type and features of the material. Equally, the whole pedagogical setting affects the usage of the learning material, in respect of adequacy and efficiency of its use. In order to answer this question we will, first, define what kind of digital learning material exists, how digital material can be classified, and how the varying features of digital material can be described. Another area for examination is how to use these materials in varying educational settings.