Gamification is viewed as an educational approach that could lead to an increased academic performance through applying game-like elements in a learning context in order to promote the acquisition of knowledge, skills, and attitudes. Despite the growing interest related to gamification, there are still considerable inconsistencies related to this concept. This chapter extends the gamification research area by offering an overview of teachers’ gamification knowledge, gamification principles, and usage of gamification principles in the teaching-learning process. Two hundred and seven k-12 school teachers (91% women), aged between 18 and 61 years old, with a mean of teaching experience of 8.68 (SD = 9.52, range from a few months of experience to 42 years of experience) defined gamification, described the principles of gamification and answered to scales measuring gamification knowledge, the representativity of some principles in gamification approaches, and the usage of gamification principles during their teaching in the past 2 years. The results of the deductive qualitative analyses showed that gamification was defined by using five themes and the data provided by participants were coded in seven gamification principles. Related to the quantitative approach, no significant differences were found in terms of gamification knowledge level, representativity of some educational principles to gamification, and principles’ gamification usage depending on various teachers’ socio-demographic characteristics. Finally, we concluded by highlighting the current status of gamification among k-12 school teachers, suggested several future research directions concerning gamification in educational contexts and presented the practical implications of these results.