Three-dimensional (3D) bioprinting is a promising technology which utilises additive manufacturing technologies to produce functional tissues and organs. A bioink is the term used to describe any biomaterial, containing cells or other biologics, which is compatible with 3D bioprinting processes. The ideal bioink is one which is biocompatible, biodegradable, can achieve high shape fidelity during and after the bioprinting process and can provide a microenvironment which can accommodate the formation of a functional biological tissue. This chapter will discuss the composition of multiple naturally derived bioinks and synthetic bioinks which are commonly used in 3D bioprinting. It will also discuss how bioink stiffness and composition can influence and direct cell fate. Finally, this chapter will demonstrate how bioinks have advanced the field of tissue engineering by highlighting some key strategies involving the 3D bioprinting of tissues such as bone, vascular tissue and liver.