Subject didactics has contact points to (1) other educational sciences such as pedagogy, pedagogical work, didactics and education studies, (2) the school subject / subject area, and (3) practical teaching (Andersson, 2000). Many areas of subject didactics have in recent decades evolved from experience-based methodology to research fields. This applies, for example, to “science didactics” (“naturvetenskapernas didaktik” in Swedish and usually “Science Education” in English), which in Sweden has developed since the mid-1980s. Over the past fifteen years, the country has received a number of new both doctors and professors within the field. Since 2002, there has been a national research school (FontD) and since 2005 a Nordic journal (NorDiNa). In 2015, Nationellt centrum för naturvetenskapernas och teknikens didaktik (NATDID) was inaugurated, with the task of supporting school development and spreading research results based on science education research. I myself have my background in “science didactics”, but I am also interested in comparing the field with other areas of subject didactics. I am particularly interested in what unites the areas, i.e. what can be called "general subject didactics" (see, for example, Brante, 2016; Hopmann, 2007; Kansanen, 2009). Comparative studies of different areas of subject didactics are usually referred to as "comparative subject didactics" (e.g., Wickman, 2012). I ask: How does "general subject didactics" relate to general didactics (“allmändidaktik” in Swedish), curriculum studies (“läroplansteori” in Swedish) and education (“pedagogik” in Swedish) on the one hand and subject-specific subject didactics on the other hand? Based on the answers to these questions, I suggest a core knowledge of "general subject didactic", i.e. knowledge areas and perspectives that are common for different areas of subject didactics. On the NOFA conference website, interdisciplinary work, teaching technology, assessment, language development, development of generic skills, values in teaching etc. are mentioned as examples of didactical areas. The question is if and when such areas are general didactics, subject didactics or "general subject didactics"? For the latter, I think that Wolfgang Klafki’s (2000/1958) five general questions about the subject matter are particularly important as indicators. They deal with the structure and relevance of the content and implications for teaching and learning in and about the subject.