Updated 14/02/19 - Corrected a typo and re-written first paragraph of page 173 (Packets) to state that packets are directed around a network by routers and not sent. This free eBook is a compilation of the lesson resources that I have written over the past two years whilst teaching this course. Besides written content and diagrams to explain concepts, I have included links to many YouTube videos that will allow pupils to go deeper into topics and learn in ways other than just reading. You should be able to simply click on the image on all “Video” pages to link to the appropriate YouTube page straight from the PDF. This eBook is released under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International license, so please feel free to share it with others - teachers, pupils or whomever you think might be interested in it! However, if you do so, please do point them back to this page as means of attribution. Other resources that might be useful to you If you do find this eBook useful, you may be interested in my YouTube channel where I have produced a number of original videos to explain Computer Science topics as well as put together playlists of great videos from other YouTubers: https://www.youtube.com/mrawdimmick Finally, if you are teaching GCSE Computer Science then you might be interested in my online Python course hosted on repl.it. As a “community” classroom you can point your students directly to it for some self-learning or you can “Import and Teach” the class into your own Repl.it Classroom for you to invite your pupils to join so that you can track their progress and provide feedback on their work: https://repl.it/community/classrooms/29589