Modern Flag Design is an expansion of Good Flag, Bad Flag: How to Design a Great Flag, first published in 2001, articulated the five principles of good flag design synthesized by Ted Kaye and the North American Vexillological Association – The Flag Experts of the United States and Canada. The distillation of the expertise of over 20 vexillologists, it has become a classic resource for those wishing to design or re-design a flag. Many flags have changed since the publication of that book, and its overall design deserved refreshing. This expansion, created with the advice and support of Ted Kaye, aims to bring more details to principles for good flag design. The five principles of good flag design that form the structure of this book are: Keep it simple, Use meaningful symbolism, Use few basic colors, No lettering or seals, Be distinctive or be related. For each principle you will find examples of good & bad design followed by a deeper analysis of one (or more flags) to sum up the chapter. Finally, you will find two detailed analysis of two flags to review all the rules around a practical case. This book is open-source and you can find all the files used in its realization via this link: https://flagdesignbook.com. It's therefore up to you to enrich it or to translate it as you wish.