Usual lunar calendar is in use due to the lunar cycle and phases, on which the whole calendar is established. Lunar calendar is the main calendar in Islam and is often referred to as the Hijri calendar. It always has 12 month in it and used mainly for religious purposes. But at the same time it can serve as a guide to gardening and harvesting activities, or a calendar for day-to-day life as in Saudi Arabia, for example. Lunar calendars are nowadays counted as actual "lunisolar" calendars – lunar cycles are counted by months, and these months would be synchronized with solar years. Lunar calendar usually has 354.37 days.
Hebrew, Hindu, and Chinese people also have been using lunar calendars since ancient times. Start day of a lunar month depends on the calendar system used: fool moon signifies start of a new month in Hindu calendar system, but Hebrew count moon crescent as a start of new month. Chinese people consider new moon as a starting point of a new lunar month.
These calendar systems do not only vary by their starting date – length of a lunar month is also different. Most months in a lunar year have about 29-30 days, length depends on whether this month is full or hollow. But please remember – whatever lunar calendar you use, it changes from year to year. So make sure to buy a new one and the end of the current year.