The study examines the impact of the Flipped Classroom (FCM) on the development of key competences for the 21st century (KC21) in future teachers. Experimental design with two parallel groups was used. The sample consisted of 122 students of the Faculty of Education, i.e., experimental group-EG (60), and control group-CG (62). The EG attended lectures implementing the FCM, while the CG received traditional instruction. Results show that there is no significant difference in self-assessment of competence development between the EG and CG related to creativity, responsible attitude towards work, health and environment. There is a significant difference in the self-assessment of competences related to socio-emotional skills, problem solving, critical thinking, information and ICT literacy and learning to learn. The conclusion is that the implementation of the FCM can influence the development of the majority of KC21.