My sister and I signed a 1 year lease 1/1/08. At the end of the year we were both to move out. My sister's plans fell through and she went back to the landlord and they agreed to a month to month lease. I was in no way involved in this. She has been there since but has not paid the rent for 11/09 and 12/09 and the landlord is taking both of us to court for eviction and nonpayment. Is he allowed to include me in this suit since I did not make this oral agreement with him?What are my options?

What state are you in?

So you moved out in 1/09? Can you prove it? If so, I would write to the landlord stating that since you moved out at the end of the lease you signed, you have no responsibility for rent after 1/09. You can add that, if he doesn't drop you from the suit, you will countersue for your costs in defending against the suit.

I am in ny. I wrote a letter already to the landlord when he served the request for payment yet he still included me in the suit.

So write him another. Tell him you will file a countersuit and do so if he still doesn't drop you.

You have proof you moved when the lease expired. Its up to him to prove that you agreed to an extension. Since he can't prove it, you should win a counter suit