Many methods exist for the preparation of ketones in industrial scale and academic laboratories. Ketones are also produced in various ways by organisms; see the section on biochemistry below.
In industry, the most important method probably involves oxidation of hydrocarbons, often with air. For example, a billion kilograms of cyclohexanone are produced annually by aerobic oxidation of cyclohexane. Acetone is prepared by air-oxidation of cumene.
For specialized or small scale organic synthetic applications, ketones are often prepared by oxidation of secondary alcohols:
Typical strong oxidants (source of "O" in the above reaction) include potassium permanganate or a Cr(VI) compound. Milder conditions make use of the Dess–Martin periodinane or the Moffatt–Swern methods.
Many other methods have been developed, examples include:
* By geminal halide hydrolysis.
* By hydration of alkynes. Such processes occur via enols and require the presence of an acid and mercury(II) sulfate (). Subsequent enol–keto tautomerization gives a ketone. This reaction always produces a ketone, even with a terminal alkyne, the only exception being the hydration of acetylene, which produces acetaldehyde.
*From Weinreb Amides using stoichiometric organometallic reagents.
* Aromatic ketones can be prepared in the Friedel–Crafts acylation, the related Houben–Hoesch reaction, and the Fries rearrangement.
* Ozonolysis, and related dihydroxylation/oxidative sequences, cleave alkenes to give aldehydes or ketones, depending on alkene substitution pattern.
* In the Kornblum–DeLaMare rearrangement ketones are prepared from peroxides and base.
* In the Ruzicka cyclization, cyclic ketones are prepared from dicarboxylic acids.
* In the Nef reaction, ketones form by hydrolysis of salts of secondary nitro compounds.
* In the Fukuyama coupling, ketones form from a thioester and an organozinc compound.
* By the reaction of an acid chloride with organocadmium compounds or organocopper compounds.
* The Dakin–West reaction provides an efficient method for preparation of certain methyl ketones from carboxylic acids.
* Ketones can be prepared by the reaction of Grignard reagents with nitriles, followed by hydrolysis.
* By decarboxylation of carboxylic anhydride.
* Ketones can be prepared from haloketones in reductive dehalogenation of halo ketones.
* In ketonic decarboxylation symmetrical ketones are prepared from carboxylic acids.
* Hydrolysis of unsaturated secondary amides, β-Keto acid esters, or β-diketones (the acetoacetic ester synthesis).  
* Acid-catalysed rearrangement of 1,2-diols, or Criegee oxidation of the same.