This course provides a beginner's introduction to the powerful and ever-more popular React.js JavaScript framework. It has been designed for anyone who is already familiar with HTML and JavaScript, and perhaps already using another JavaScript framework, but wanting to understand the basics of React.js. React.js is quite a significant departure from most other JavaScript frameworks and it can be tricky to "get it". Key to "getting" React.js is understanding its key underlying concepts, so that's what this short course will focus on, through a mixture of diagrams and the creation of a simple working application.