A sale agreement is generally concluded when there is an agreement as to the object and the price of the sale. This agreement can take all forms available for concluding contracts; it can even be concluded orally. However, in practice, contracts are usually concluded in writing.
(Special feature: sale agreements between spouses have to be concluded by way of a notarial act.)
In practice, and especially when an estate agent is involved, the sale agreement is often concluded in the form of a written offer submitted to the interested party, which the owner of the property accepts in writing (written sale agreement).
As ownership is not transferred when the contract is concluded, but only when it is registered in the Land Register, the documents to be presented to the Land Registry have to comply with the conditions applicable to content and form. This particularly implies that the signatures of the deed of sale have to be certified.
It is also possible, but rare, to draw up a so-called act of “Punktation” (Punktationsurkunde), that is an act signed by the seller and the buyer regarding the main elements of the sale, specifically the object and the price of the sale. In that case, the seller and the buyer agree on a later date to draw up a more formal and complete act (authenticated act, clean copy).
It is also possible, but again unusual, to conclude a preliminary contract, i.e. an agreement to conclude a main contract in the future.