This chapter discusses two major chemical reactions of aldehydes and ketones. Reaction of nucleophiles with an aldehyde or ketone gives an alkoxide via acyl addition. Subsequent hydrolytic workup gives an alcohol. The carbonyl of aldehydes and ketones reacts as a Brønsted-Lowry base with a suitable acid to generate an oxocarbenium ion intermediate. An acyl addition reaction with an unsymmetrical ketone will create a stereogenic center. Acyl addition reactions of Grignard reagents with aldehydes or ketones give an alkoxide product, but there is no reactive intermediate. An important method to improve the reaction exploits the acid-base chemistry of aldehydes and ketones. The cyanide ion was shown to be a moderate nucleophile in acyl addition reactions.