Malacology is the branch of invertebrate zoology that deals with the study of the Mollusca (mollusks or molluscs), the second-largest phylum of animals in terms of described species after the arthropods. Mollusks include snails and slugs, clams, octopuses and squid, and numerous other kinds, many of which have shells. One division of malacology, conchology, is devoted to the study of mollusk shells. Malacology derives from Greek μαλακός, malakos, "soft"; and -λογία, -logia.
Fields within malacological research include taxonomy, ecology and evolution. Applied malacology studies medical, veterinary, and agricultural applications; for example, mollusks as vectors of disease, as in schistosomiasis.
In 1681, Filippo Bonanni wrote the first book ever published that was solely about seashells, the shells of marine mollusks. The book was entitled: Ricreatione dell' occhio e dela mente nell oservation' delle Chiociolle, proposta a' curiosi delle opere della natura, &c. In 1868, the German Malacological Society was founded.
Zoological methods are used in malacological research. Malacological field methods and laboratory methods (such as collecting, documenting and archiving, and molecular techniques) were summarized by Sturm et al. (2006).