t hard. The original idea was to write a book about 'IPv6 Multihoming', a topic we touch on in Chapter 6 of this book. In August 2010 Teemu and Jouni were working in a joint Finnish TEKES-funded research project called 'Wireless Broadband Access (WiBrA)', and Teemu came to ask if Jouni would be interested in co- authoring a book about 'Advanced IPv6 Multihoming'. Jouni was interested, but was also proposing a slightly different focus for the book. During 2010 and 2011 Wiley approached us periodically, and patiently reminded us to send a detailed proposal for a book. It took quite some time to get into grips with and actually write the book proposal, as we were both busy working with practical IPv6 matters of our employers, doing research under WiBrA, and spending time with IETF and 3GPP standardization activities. In retrospect pieces of the puzzle seem to have fallen into place rather nicely, as the time we did not manage to write a book proposal, was mostly spent on gaining actual experience and knowledge which have significantly affected the details of this book. In fall of 2011 Teemu and Jouni got more into actually progressing the book, and approached Jonne with a request to be the third author. We all knew each other from the past, as we had all been working for Nokia or Nokia Siemens Networks at the same time. With the three of us we thought we would have wide enough skill-set and experience to write the book: Teemu had the background on the handset implementations, Jouni had the background on cellular network operations and network equipment implementation, and Jonne had the background from being a long-timer in network equipment implementation and IPv6. All of us had been active in 3GPP and IETF standardization, with Jonne being involved in 3GPP already when IPv6 got hammered into 3GPP standards. Together we had more than three decades of experience of IPv6. With three of us together, we started planning to write a 150-200 page book, but it soon increased to close on 400 pages. At the same time the scope