Abstract. This article sketches a theoretical framework that I have been devising in order to teach the nature of science (NOS) to pre- and in-service science teachers for all the educational levels (from kindergarten to university). The framework suggests that teachers should learn a set of simple 'key-ideas' from NOS. Those key-ideas can be selected and validated through a matrix that has two 'structuring' components: 1. A list of the main schools of twentieth-century philosophy of science (called stages ); and 2. A list of their main fields of inquiry (called strands ). Examples of NOS contents within and across some of the three stages and seven strands that I have identified, together with suitable pedagogies, are presented here under the form of three didactical units. NOS as a research focus in didactics of science The philosophy, history, sociology, psychology and linguistics of science are sometimes called meta-sciences , using the Greek prefix 'met' with the meaning 'beyond', since they constitute second-order reflections on science as a product and as a process (Estany, 1993). In this sense, didactics of science (i.e. science education as a discipline) can also be considered meta-scientific in part (Adriz-Bravo, 2001c). The importance of meta-sciences for science education has been acknowledged by educational researchers, policy makers and science teachers (AAAS, 1989; Matthews, 1994; Driver et al., 1996; NRC, 1996; Millar and Osborne, 1998). Accordingly, rationales and proposals have been put forward in the last twenty-five years with the aim of teaching conceptualisations on the nature of