In this chapter, we look at ways in which we can model both tissue and its interaction with cells, water and blood. This interaction is key to understanding many different types of physiological behaviour, since most tissue is fundamentally very soft and thus deforms easily. We will examine how to model tissue metabolism in terms of the diffusion and usage of oxygen. Finally, we will consider how more complex models can be built across multiple scales, for example to combine cellular and tissue behaviour. This chapter shows how we can use engineering tools to investigate this behaviour and examines a few very simple cases.