This document discusses pattern libraries and their workflow. It begins with recapping atomic design principles of atoms, molecules, organisms and templates that make up a style guide. It then defines a pattern library as a style guide combined with reusable code components. Examples of popular pattern libraries are provided, including from Mailchimp, Bootstrap and others. The document stresses that consistency through reusability is key to efficiency for clients, designers, programmers and managers. It concludes that pattern libraries allow non-coders to graphically assemble pages like Lego without touching any code.