Several research studies have been conducted with novice and experienced teachers when teaching within and outside their subject specialism. This paper aims to review a number of these studies and highlights key points concerning the teaching of different science subjects at secondary level and teachers' level of self-confidence. Teachers face considerable challenges when teaching outside their area of expertise. These challenges are mainly due to limited subject matter knowledge (SMK) in a particular science area. This will also influence the development of the teachers' pedagogical content knowledge (PCK) which is crucial in lesson preparation and in the way science teaching is conducted. Teachers have also developed a number of strategies to deal with such challenges.