It is proper to finish eating or disposing of all of one’s hametz before Passover, but in practice this sometimes proves difficult. It is especially unfeasible for stores and factories that maintain a large inventory of hametz, as well as homes which have expensive hametz products, such as special whiskeys. Therefore, the Sages instituted the sale of hametz, whereby one’s hametz can be sold to a non-Jew for the week of Passover.

Due to the concern over finding hametz on Passover, and given the severity of the prohibition, everyone, even someone who has cleaned his house well and removed all hametz of which he is aware, should sell his hametz, in case there is hametz in his possession of which he is unaware.

From a halakhic perspective, this sale is complicated, and the contract is highly complex, since the transaction must comply with all the criteria of halakha as well as the laws of the country in which the sale takes place. In practice, the seller signs a document which he can get from his local synagogue rabbi. This document empowers the rabbi or his representatives to sell to a non-Jew any hametz that is found at the address specified in the document. The transaction requires a halakhic act of acquisition. Usually this is done by the rabbi handing the seller a pen, which is a symbolic act of exchange.

One who does not live near a rabbi or does not know where he can make the sale in person can do so over the internet or by phone.

At the time of the sale, the non-Jew pays a symbolic down payment for all the hametz in the transaction, while agreeing that after the holiday he will pay the actual value of the hametz being bought.

In practice, at the end of Passover the rabbi buys back the hametz and it returns to our possession. Thus, all sides benefit from the arrangement. In principle, if during the course of the holiday the non-Jew would want to actually pick up the hametz and take it home, he may do so, but then he would have to pay the full cost of those products.

All the products that are sold as hametz should be put in specific locations in the house, closed off, and marked as hametz.

The sale of hametz must be completed by the morning of the day before Passover, before the latest time allowed for the burning of hametz. Any hametz that was not sold to a non-Jew but remained in the possession of a Jew over the holiday is referred to as “hametz over which Passover has elapsed,” and its consumption, as well as deriving any benefit from it, are prohibited, even after Passover.

One who leaves his home some time before Passover to spend the holiday elsewhere can leave instructions before his departure to carry out the sale, which will take effect at the usual time and be in force until the end of the festival.