Drug discovery is a lengthy and very expensive endeavour. Many computational methods have been introduced in this book with the aim to tackle challenges in drug discovery. The motivation here is not just to save time and money, but also to assist in prioritising and optimising compounds for synthesis based on asking scientific questions and attempting to answer them with these methods. However, the true validation of computational methods is reduction to practice. This section summarises some key computational methodologies applied in drug discovery and medicinal chemistry. The section works through the drug discovery process from target validation and hit discovery, through to moving those hits into lead compounds, and finally the optimisation of those leads into potentially successful clinical candidates.