Under certain conditions, a ketone having an alpha-hydrogen atom may be acylated with an ester, an acid anhydride, or an acid chloride to form a β-ketone or, when the acylating agent is a formic ester, a β-keto aldehyde. The process consists in the replacement of an alpha-hydrogen atom of the ketone by an acyl group. The reaction involves a carbon-carbon condensation. The acylation of ketones with esters has generally been effected by means of a basic reagent, such as sodium, sodium ethoxide, etc. The acylation of ketones to form β-diketones may also occur with acid anhydrides by means of an acidic reagent boron trifluoride. In this chapter the basic reagent and boron trifluoride methods of acylation are considered separately. They are compared with other methods.