The piperidine catalyzed reaction of benzaldehyde with ethyl benzoyl acetate leads to formation of a trisubstituted carbon-carbon double bond compound: ethyl benzylidenebenzoylacetate, I. This reaction, first discovered by Knoevenagel, and bearing his name, has been repeated numerous times in the literature and is representative of a class often used in the synthesis of agents of biological interest. The stereochemistry of I has remained to be determined but was frequently assigned, a priori, Z (I-Z). The synthesis of I was repeated but its stereochemistry was unresolved using 1H NMR NOE. X-ray crystallography however showed I to be E (I-E). Attempts to isomerize I-E to I-Z were not successful. Calculations indicate I-E to be 7.7 Kcal/mol more stable than I-Z. Efforts to repeat a literature preparation of I-Z and to isomerize it to the more stable I-E, will be discussed as well as a mechanism leading to formation of I-E. The stereochemistry of several related compounds will also be described.