After Purim is the beginning of our Pesach preparations. We are thinking about what we'll serve for our seders, who we'll invite, and cleaning the house. On Pesach, we aren't merely refraining from eating chametz or even not benefiting from chametz, we are not even allowed to own chametz. Food that we have and the dishes that we cook with must be disposed of in some manner.
In the Middle Ages, Jews who owned bakeries and breweries were left with large inventories of chametz, so in order to get around the prohibition of owning chametz, they sold their inventories to non-Jews. Over the centuries, as people became richer and owned more, individuals followed the businessmen's lead and also sold their chametz to non-Jews. Even in the 19th century, it was common for individual Jews to sell their chametz to non-Jewish friends.
However, the laws of the sale must be performed in a particular manner in order. To prevent individuals from doing invalid sales (and thus still owning chametz on Pesach), the local Rabbis started to handle this function. We now give the local Rabbi the Power of Attorney to sell our chametz for us.
We have placed our Chametz Sales form on our website. However, if you prefer, you can also download the paper form.