Despite the fact that co-ownership is a very popular form of landholding in Singapore, many aspects of the law relating to it remain unsettled. This article explores the question whether the granting of a mortgage or a lease by one joint tenant severs the joint tenancy. It is argued that in deciding this matter the courts should have regard to the fact that modern law provides a simple and effective means of severance. The courts should not therefore be astute to discover new methods of severance and in particular should avoid any forms of severance which can be effected by one party without the knowledge of the other joint tenants.