Doctor Andy's Rule Language (DARL) is a computer language intended to encode knowledge as fuzzy logic rules. It is an extremely simple language, and designed to be used with little training. It is intended to be a simple way to represent business or professional knowledge of both logical and numeric kinds, while permitting the representation and processing of various kinds of uncertainty. This book describes the technologies behind DARL, the language itself, and how to write your own rule sets. It is also a guide to the various support tools, the online editor and testing systems and the online inference engine. It contains several worked examples, as well as descriptions of how to access the REST interfaces that embody the online inference engine from a variety of technologies including websites, apps, and especially Logic Apps inside Microsoft Azure. Uniquely, You can use machine learning to create DARL rule sets, which is described in the text, and uniquely again, you can use the DARL inference engine as an intelligent forms engine, targeted at applications too difficult for Survey Monkey and similar services. Again how to do this is fully described with examples.