Within the last decades, there has been an increasing interest in the creation of learning environments that emphasise science practices as a means to achieve scientific literacy. This thesis targets one practice: the construction of explanations. To successfully integrate this practice into their classroom, teachers need a particular body of knowledge known as Pedagogical Content Knowledge (PCK). There are virtually no existing studies whose goal is to conceptualise teachers’ PCK of scientific explanation. To address this gap, I embarked in a research project driven by the following questions: (Q1a) What ideas, knowledge, and beliefs do teachers hold about scientific explanation?; (Q1b) In what instructional practices do science teachers engage during science lessons to support students in constructing scientific explanations?; (Q1c) How do teachers assess students’ attempts to construct explanations?; and (Q2) What do teachers perceive to be the fostering and/or hindering conditions for the teaching of scientific explanation construction in the classroom? I designed a multi-participant exploratory case study approach to solving these questions. Five science teachers from three Secondary schools in Spain and England volunteered to participate. Main data sources included audio-recorded lessons, semi-structured interviews and fieldnotes. Data analysis occurred in multiple steps, being informed by thematic and constant comparative techniques. First, each case was examined separately. Findings from this analysis were presented in the form of participants’ case profiles. In a second stage, a cross-case analysis was conducted to identify common patterns among the cases. This allowed for the development of five key assertions: (1) Teachers display a multiplicity of meanings for ‘explanation’; (2) Despite being identified as an essential scientific practice, explanation construction –as I have operationalised it– is rarely purposely integrated into instruction; (3) Teachers rarely display specific instructional sequences to promote the construction of scientific explanations. However, they use some strategies to interact and guide students in explanatory episodes; (4) Teachers do not possess specific assessment models for the construction of explanations; and (5) Teachers identified some inhibitors for designing environments in which explanation-production plays a significant role, including large-size classes, crowded syllabi, and a lack of resources and experience. The participants also noted some fostering conditions, including teachers’ confidence, autonomy, and support from the school’s management team, other teachers, and parents. These findings were discussed in terms of their implications for teacher preparation, research, and practice. Finally, some potential limitations were identified.