In Outlook, customers can create individual calendars for work, family, and other purposes, and organize them in calendar groups. They can turn on the free Birthdays and Holiday calendar to remind them of contacts' birthdays and local holidays. They can add calendars that match their interests, such as calendars for sport teams and TV programs. Customers can select and overlay calendars, and see their events in the same view. Through the calendar API, your app can similarly organize calendars in calendar groups, and interact with interesting calendars just like any other calendar in the user's mailbox.