If I am a member of multiple organizations do I need multiple usernames/passwords?

No.  You should only ever have 1 username and 1 password. It is actually a violation of our terms of service to have more than 1 username or password with our system.  Having 1 username and password will get you access to all the information you need for any organization with our systems. You can manage 1 availability calendar or multiple availability calendars - that's up to you. Some users like to manage just 1 calendar for all their organizations. However, some users like to have different calendars for different organizations.

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