Claisen-Schmidt Condensation (aldol condensation)

(from wikipiedia)

An aldol condensation is an organic reaction in which an enolor an enolate ion reacts with a carbonyl compound to form a β-hydroxyaldehyde or β-hydroxyketone, followed by a dehydrationto give a conjugated enone.

In its mechanism, it involves the nucleophilic addition of a ketone enolate to analdehyde to form a β-hydroxy ketone, or "aldol" (aldehyde + alcohol), a structural unit found in many naturally occurring molecules and pharmaceuticals.

An aldol condensation differs from an aldol reaction in that a H20 molecule is lost to form a C=C double bond.

While an aldol reaction involves a nucleophilic addiction of a ketone enolate (nucleophile) to an aldehyde, where the H of a C=C bond attaches to the O=C of the aldehyde to form OH and the C= of nucleophile bonds with C of aldehyde to form a C-C single bond.

(Diagrams always speaks clearer than words =))