Immunotherapies are the most rapidly growing drug class and have a major impact in oncology and on human health. It is increasingly clear that the effectiveness of immunomodulatory strategies depends on the presence of a baseline immune response and on unleashing of pre-existing immunity. Therefore, a general consensus emerged on the central part played by effector T cells in the antitumour responses. Recent technological, analytical and mechanistic advances in immunology have enabled the identification of patients who are more likely to respond to immunotherapy. In this Review, we focus on defining hot, altered and cold tumours, the complexity of the tumour microenvironment, the Immunoscore and immune contexture of tumours, and we describe approaches to treat such tumours with combination immunotherapies, including checkpoint inhibitors. In the upcoming era of combination immunotherapy, it is becoming critical to understand the mechanisms responsible for hot, altered or cold immune tumours in order to boost a weak antitumour immunity. The impact of combination therapy on the immune response to convert an immune cold into a hot tumour will be discussed.