THIS IS THE FINAL UPDATED OCTOBER 2018. Buy the paperback from Amazon and get Kindle eBook FREE using MATCHBOOK. go to www.usgovpub.com to learn how. Blockchains are immutable digital ledger systems implemented in a distributed fashion (i.e., without a central repository) and usually without a central authority. At its most basic level, they enable a community of users to record transactions in a ledger public to that community such that no transaction can be changed once published. This document provides a high-level technical overview of blockchain technology. It discusses its application to electronic currency in depth, but also shows its broader applications. The purpose is to help readers understand how blockchains work, so that they can be appropriately and usefully applied to technology problems. Additionally, this document explores some specific blockchain applications and some examples of when a blockchain system should be considered for use. Why buy a book you can download for free? We print this book so you don’t have to. First you gotta find a good clean (legible) copy and make sure it’s the latest version (not always easy). Some documents found on the web are missing some pages or the image quality is so poor, they are difficult to read. We look over each document carefully and replace poor quality images by going back to the original source document. We proof each document to make sure it’s all there – including all changes. If you find a good copy, you could print it using a network printer you share with 100 other people (typically its either out of paper or toner). If it’s just a 10-page document, no problem, but if it’s 250-pages, you will need to punch 3 holes in all those pages and put it in a 3-ring binder. Takes at least an hour. It’s much more cost-effective to just order the latest version from Amazon.com This book includes original commentary which is copyright material. Note that government documents are in the public domain. We print these large documents as a service so you don’t have to. The books are compact, tightly-bound, full-size (8 ½ by 11 inches), with large text and glossy covers. 4th Watch Publishing Co. is a Service Disabled Veteran-Owned Small Business (SDVOSB).