This chapter explores in detail the professional challenges, criteria, and principles for selecting, creating, and preparing materials and tasks for language learning. Teachers must not only be able to utilise and evaluate the language learning materials available, including those in coursebooks but also engage in a profound professional reflection on the choice of texts and language learning exercises, activities, and tasks, and ways of working with them. Beyond such critical reflections, teachers also need to be able to develop materials and design tasks both independently and in collaboration with other teachers. Therefore, this chapter discusses typologies of tasks, a model of the complex task, and potential strategies for assessing outcomes of complex tasks.