Tumours contain a mixture of cancerous cells and various ‘normal ‘ cell populations derived from the host which may support the growth of the tumour cells. These ‘normal’ cell populations include component cells of the vasculature, other stromal cell populations such as cancer associated fibroblasts and various bone marrow derived cells including macrophages, granulocytes, and various immune cells. These various ‘normal’ cell populations and their interactions with the tumour cells provide the microenvironment within the tumour and play an important role in tumour growth and response to treatment. In this presentation I will discuss some aspects of the tumour microenvironment, particularly the microvasculature, and how it may impact on tumour treatment response.