The primary acquisition avenue is through the purchase of new flats directly from the HDB. Over the years, various forms of sale programmes has been in place, with the current mode of sale known as the Build-To-Order (HDB) programme launched in 2001. This is run alongside the Sale of Balance Flats (SBF) exercise which handles the sale of balance flats from earlier BTO exercises, unsold SERS replacement flats and flats which were repossessed by the HDB. The sale of EC and DBSS flats are conducted separately by the respective private developers.