This analysis is based on the classification of the systems GreyNet, OpenSIGLE, Czech ASEP, RIV and others. During the analysis of the lists of document types, we have discovered that these typologies contain, besides "real" document types (reports, theses, etc.) other aspects, such as events (arrangement, organization), types of events (conferences, speeches), producers (universities, institutes), processes (translations, output), content (political documents, legal texts), location (domestic, foreign), and format (e-texts, numeric data). However, this approach is not systematic. Therefore, we have decided to create a classification scheme for document types only, and classify other aspects into various groups in order to define them more precisely. The scheme will be processed in a text version as well as schematically in mind maps. We believe that identifying a specific typology for credible grey literature document types, particularly reports, conference proceedings, and government documents, will assist in the classification of grey literature in the fields of science, research, and education. On the other hand, grey literature also consists of various means of communication, such as telephone calls, meetings, e-mails, blogs, interviews, social networking tools, or discussions in Wiki. It is important to identify only credible document types and not use unverified information that may be unsuitable for scientific work. The aim of this analysis is therefore to create, define, and implement a current credible grey literature document typology, in order to open discussions in the grey literature community, leading to a means of collecting GL from reputable events and producers rather than relying on social networking tools or Wiki contributions. While the later types of sources can assist researchers, scientists, and teachers with their information-seeking pursuits, document of this nature needs to be evaluated on a regular basis.