The question of "how much information" there is in the world goes back at least to the time when Aristotle's student Demetrius (367 BC-ca. 283 BC) was asked to organize the Library of Alexandria in order to quantify "how many thousand books are there" (Aristeas, ca. 200 BC, in Charles, 1913, Section 9). In 1949, one year after his seminal (1948) publication that both created and solved most fundamental problems of information theory, the intellectual father of what is known today as the "information age," Claude Shannon took a pencil and a piece of notebook paper and estimated the order of magnitude of the largest information stockpile he could think of. He used his newly proposed measure of information (which was at that time, quite unknown) called " the bit," and estimated the Library of Congress to contain some 10 boolean AND 14 bits (Gleick, 2011, p. 232). Pressed by the exploding number of information and communication technologies (ICTs) that fallowed the theories of Shannon and his colleagues during the decades to come, several research projects have taken up this question more systematically since the 1960s. In the eight articles of this Special Section, authors of some of the most extensive of those inventories discuss findings, research priorities, advantages, and limitations, as well as methodological and measurement differences in their approaches. The goal is to provide an open and transparent academic dialogue that deepens the understanding of the nature, assumptions and limitations of these kinds of inventories and to create a solid fundament for potential future exercises of a similar kind.