Selling jointly held property

It depends on just how title is held.  If it is as "joint tenants with right of survivorship" (JTWROS), then no, you cannot just sell without contacting the other owner.  You would need their consent.  If you own as "tenants-in-common", then you can sell, transfer, or otherwise encumber your interest freely. 

Note:  If the deed is silent as to how title is held, the judicial preference it for it to be considered as tenants-in-common; this promotes the transferability of property.  Not withstanding the foregoing, marital property is considered to be held as joint tenants.

If a trust, business entity, or other form of joint ownership is involved, the operable instrument would dictate your rights in the event of a sale.