Book excerpt: Modern society is rapidly becoming fully digitalized. This has many benefits, but unfortunately, it also means that personal privacy is threatened. The threat does not so much come from a 1984 style Big Brother but rather from a set of smaller big brothers. These small big brothers are companies that we interact with - public services and institutions - and that we invite to our private data. Privacy as a subject can be problematic as it is a personal freedom. In this book, we do not take a political stand on personal privacy and what level of personal freedom and privacy is the correct one. The text instead focuses on understanding what privacy is and some of the technologies that may help us to regain a bit of privacy. It discusses what the different aspects of privacy may be and why privacy needs to be there by default. There are boundaries between personal privacy and societal requirements, and inevitably society will set limits to our privacy (Lawful Interception, etc.). There are technologies that are specifically designed to help us regain some digital privacy. These are commonly known as Privacy Enhancing Technologies (PETs). Aspects of Personal Privacy in Communications investigates some of these PETs, including MIX networks, Onion Routing, and various privacy-preserving methods. Other aspects include identity and location privacy in cellular systems, privacy in RFID, Internet-of-Things (IoT), and sensor networks amongst others. The text also covers some aspects of cloud systems.