Aldol reactions constitute a powerful methodology for carbon-carbon bond formation in synthetic organic chemistry. Biocatalysis by means of aldolases offers a unique stereoselective and green tool to perform this transformation. Recent advances in the field, fueled by either protein engineering or screening, greatly improved the number of synthetic opportunities from small chiral polyfunctional molecules to highly complex oligosaccharide analogs with potential pharmaceutical relevance. Furthermore, aldolases have been shown to be particularly valuable for obtaining new types of structures (i.e. generate molecular diversity) accessible for investigations in drug discovery. Extensive knowledge arising from biochemical studies and synthetic applications of natural aldolases has fostered the development of novel catalysts, such as the de novo computational design of aldolase enzymes, aldolase ribozymes, or synthetic peptides and foldamers with aldolase activity, outlining first steps toward the creation of tailor-made (bio)catalysts to suit any desired application.