This chapter examines and discusses how nine mathematical modellers have learned mathematical modelling and their opinions on mathematical modelling in upper secondary education. Based on interviews it was found that they mainly learned mathematical modelling during their PhD studies and through their occupation, by working with ‘real modelling’. Their opinions are that mathematical modelling should be a part of mathematics education in upper secondary school, in particular should modelling be more emphasized as a part of general education to develop students’ critical views on how models are used in the society. In addition, they gave suggestions for approaches to teach modelling and suitable modelling problems to work with from their own workplace.