Markush structures in chemistry were named after Eugene Markush, the first inventor to include them successfully in a U.S. patent, in the 1920s.

In general, a Markush structure is a chemical structure with multiple "functionally equivalent" chemical entities allowed in one or more parts of the compound. According to "Patent Law for the Nonlawyer" (Burton A. Amernick; 2nd edition, 1991),

"In claims that recite... components of compositions, it is sometimes important to claim, as alternatives, a group of consitituents that are considered equivalent for the purposes of the invention.... It has been permissible to claim such an artificial group, referred to as a 'Markush Group,' ever since the inventor in the first case... won the right to do so."

If a compound being patented includes several Markush groups, the number of possible compounds it covers could be vast. No patent databases generate all possible permutations and index them separately. Patent searchers have the problem, when searching for specific chemicals in patents, of trying to find all patents with Markush structures that would include their chemicals, even though these patents' indexing would not include the suitable specific compounds. This is where databases that permit searching of chemical substructures are indispensable.