In keeping with its character as evasive and subversive language, slang is hard to define. Some see it as urban masculine vocabulary focused on sex, intoxication, and excretion; others as instrumentally valuable in the construction of in- and out-groups, or as a matter of style to facilitate fitting in and standing out. This chapter traces the history of slang dictionaries from the first slang dictionary of 1699, written by the semi-anonymous ‘B. E.’, to the work of other slang lexicographers throughout the centuries: Francis Grose, John Camden Hotten, John Stephen Farmer, William Ernest Henley, Eric Partridge, Jonathan Lighter, and Jonathan Green.