It is important to clarify the general conditions first. Is it a private or listed company? What form do the shares take? The shares almost always have to be legally assigned. This works with a declaration of assignment. This must be signed in a legally valid form. However, if the shares are in the form of a token (“register value right”) or as a depositary share, no declaration of assignment is required. In this case, the transfer of the token or the shares in the banking system is sufficient. In the case of a private company that is not listed/quoted, a share purchase agreement may make legal sense.