This tutorial provides an overview and a practical experience on task models based engineering of interactive systems. It highlights how the recent advances in task modelling techniques can be exploited to design, develop and assess interactive systems. We present, from an engineering perspective and using examples from industrial case studies, how task models can support the design, development and evaluation of interactive systems. Furthermore, half of the tutorial focuses on the process of customizing task modelling notations for specific engineering needs and on its application using the tool supported HAMSTERS-XL notation.