The main body of the book gives a huge amount of historical and folkloric information on every day of the year (including, yes, February 30, which has happened three times); the days of the week, months and seasons; and the major feast days and festivals in a wide variety of different cultures. This is the section that most readers will find the most fascinating; its 658 pages provide endless browsing.
The second part concentrates on the making of calendars over the centuries: how our own complex calendar evolved with its irregular month lengths and its rules for when leap years occur, plus details of the calendars of many other cultures--Chinese, Hindu, Muslim, and many more--all trying to find a regular system that can cope with the fact that the roughly 29-and-one-half-day lunar month and the roughly 365-and-one-quarter-day solar year simply can't be meshed.
Bonnie Blackburn and Leofranc Holford-Strevens must be congratulated on the huge amount of work this book must have taken, and on such splendid results. --David V. Barrett, Amazon.co.uk