Bifurcation theory is concerned with systems that have a parameter that can be varied. As the parameter changes, the qualitative behaviour of the system, for example the number of fixed points or their stability, will normally stay the same if the variation is small. But at certain parameter values, the behaviour of the system may change significantly. This is called a bifurcation. It turns out that there are only a few standard types of bifurcation that commonly occur across different systems. This chapter aims to explain why this is the case, and describes these standard types of bifurcation.