Throughout history many civilizations developed calendars based on 12 months. In general one month is approximately how long it takes the moon to orbit around the earth and one year is how long it takes the earth to orbit around the sun.
Civilizations based their calendars on the sun and others the moon. The lunar calendar is helpful if you want to follow the phases of the moon. The solar calendar is helpful if you want to keep track of seasons. Many people think that the Islamic calendar is a lunar calendar but on closer examination of the meanings of the Islamic months, it is clear that they are based on seasonal events. However it is not a solar calendar. The Quran tells us to rely on the phases of the moon to plan our calendar.
So what type of calendar is it then? There is a third alternative called the lunisolar calendar. This type of calendar has advantages of both the lunar and solar types of calendar. It follows the moon phases while keeping months and seasons in sync. It relies on the sun and the moon just like it is suggested in the Quran.
Here is a detailed explanation of the Islamic calendar! Very interesting!