A Co-sign Lease Agreement is a legally binding document between two or more parties that outlines the terms, conditions and responsibilities of the lease. It defines who is responsible for the payments, rent increases, repairs, and other aspects of the agreement. The co-signer agrees to take responsibility for the lease if one of the parties fails to pay or comply with the contract. This provides landlords with an additional layer of security and assurance since the co-signer will bear full financial responsibility for any unpaid bills or costs related to the lease. By signing this agreement, both parties agree to abide by its rules and adhere to all the details included in it.