Leviticus 23 lists all of the annual Holy Days that God commanded for mankind to observe, and it provides us with the exact months and days of the year that they are to be observed.  How do we determine when exactly these dates occur?  How does the Biblical calendar work?  Many believe the Biblical calendar is a very complicated subject, but scripture reveals a surprisingly simple system for determining the calendar.  The key to the Biblical calendar lies in answering three simple questions: How does the Bible define a day?  How does the Bible define a month?  How does the Bible define a year?  This paper explains the simple answers to these questions and also addresses many of the issues that are often raised to confuse this simple subject.