Molecular model kit: A set of parts, usually of plastic, that can be used to construct models of molecules. (Computer imaging has replaced traditional molecular model kits in many applications, but extracting three-dimensional information from a two-dimensional image on a computer screen requires a good understanding of basic three-dimensional molecular structure from the start.) An essential tool for everyone who thinks about organic chemistry, from student to pharmaceutical professional to professor. The best students always reach for their model kit when thinking about three-dimensional structure, a fundamental concept in organic chemistry.