Do I have to tell my landlord I am moving if I have a written lease?
No. Your lease sets forth the date on which it ends, and you are supposed to move on that date unless you and your landlord agree to renew your lease agreement.

What if I do not have a written lease?
If you pay rent on a monthly basis, you must give your landlord 30 days written notice that you are moving out. Otherwise, you can be held liable for another month's rent. If you pay rent on a weekly basis, you give your landlord 7 days written notice that you are moving. Otherwise, you can be held liable for another week's rent. For more information, see the Leases and Subleases Guide.

Does every tenant have a lease agreement?
Yes. It may be a written lease or an oral (unwritten) lease.

What is the advantage of a written lease agreement?
It sets out the terms of your agreement with the landlord. Furthermore, it states how long your tenancy will last, and your landlord cannot terminate this tenancy early unless you violate one of the lease provisions.