Tissue growth is highly dependent on the supply of oxygen and nutrients. This regulatory mechanism does not only apply to normal tissue but also to tumour tissue. In contrast to normal tissue, a tumour at the initial stage is not vascularised. Thus, further expansion requires that the tumour creates its own blood vessel supply. In this context, it is well established that tumours can induce capillary sprouting from pre-existing, surrounding vessels. For many years, it was believed that tumour vascularisation is exclusively due to this process. However, recent studies have revealed complementary mechanisms and processes, such as intussusceptive angiogenesis and postnatal vasculogenesis, as well as alternative mechanisms, like vessel co-option and vasculogenic mimicry. Furthermore, several cellular and molecular mechanisms mediating the switch from a non-angiogenic to an angiogenic phenotype have meanwhile been identified and targeting key molecules has become a novel strategy to treat malignant diseases. This review briefly summarises the current knowledge on molecular and cellular aspects of tumour vascularisation to emphasise the complexity of the vascularisation process.