In recent years, sustainability has become more important for fast fashion companies to embrace. Partly because of climate change and partly because consumers’ demands are higher. To make a real difference, fast fashion companies need to communicate sustainability clearly, and consumers need to be receptive to this type of communication. Thereby, both fast fashion companies and consumers have responsibilities towards the environment. However, previous research shows that consumers lack comprehension of sustainability communication within the fast fashion industry. This leads to consumption of non-sustainable clothing items over sustainable clothing items. Based on the aforementioned, three main concepts were identified as pertinent to build upon, encompassing subconcepts. The main concepts are sustainability communication, consumer comprehension and purchasing decisions. The subconcepts are says what, to whom, motivation and engagement, word recognition, language comprehension, knowledge, intentions and action.  As previous research is scattered, this research is conducted to give a gathered understanding. The purpose of this research was to examine consumer comprehension of sustainability communication within the Swedish fast fashion industry. Additionally, considerable emphasis lay on purchasing decisions. To successfully do this, the primary data was collected through a pilot study and focus groups. More specifically, there were four focus groups with six participants in each.  The empirical findings, together with the literature review, concluded that consumers recognise environmental labels and designations but do not know what they stand for. Further, sustainability communication is placed in a positive category, despite lack of comprehension. The level of motivation and engagement is low, due to suspicions of greenwashing, among other things. Language comprehension was found to have no major impact on consumer comprehension of sustainability communication. Some felt that the communication should be concise and others felt that it should provide a broader perspective. Moreover, consumers notice the sustainability communication, however, they do not seek nor respond to it. These conclusions intend to create value for fast fashion companies.