The tenant enters into a written letting agreement with the owner of the house, renting the house for eg for 1000 per month. The agreement is that they rent the house for two or three years. At the end of the term they have an option to purchase the house for a set amount of money. If they exercise the option to purchase the rent they paid can be set off against the purchase price. So if they rented at 1000 per month for three years they have 36000 paid off of the purchase price, which can be the 'deposit'. It gives people who are renting anyway the opportunity to have their rent set off against the purchase price, but if they don't want to buy they don't have to exercise the option. Obviously if they don't exercise the option to purchase they do not get the rent back. The owner takes the risk that the set price for the house fairly represents the market value in two or three years time- but the buyer has no such risk because they don't HAVE to buy.