Despite its initial promise, immunotherapy against cancer has exhibited limited success in the clinic. This indicates the need for synergistic and safer therapies causing fewer immune-related toxicities. The EU-funded ImmunoBioSynth project proposes to design synthetic biomaterials for instructing the immune system to fight cancer. These innovative biomaterials will replace biological drugs and contribute to the remodelling of the tumour microenvironment from a suppressive into a susceptible state. Ultimately, this will lead to more specific treatments that alone or in combination with other regimens can improve the outcome of cancer patients.