The first learners' dictionary was The Idiomatic and Syntactic Dictionary of English by A. S. Hornby in 1942. Hornby's dictionary was republished as A Learner's Dictionary of Current English by Oxford University Press in 1948. The second edition came in 1963, the third in 1974, both in several impressions. The dictionary was a huge financial success. This unparalleled success was, of course, the result of the boom in the English teaching (ESL, EFL) industry.
The Longman Dictionary of Contemporary English was published in 1978. The editors, led by Paul Proctor, introduced several innovations. The most striking was the use of a restricted 'defining vocabulary'. Almost a decade later another new player the Collins Cobuild English Dictionary came out, a significant milestone in corpus-based lexicography.
1995 was the 'year of the dictionaries': Oxford published its fifth edition, Longman its third, Cobuild its second and yet another player appeared, the Cambridge International Dictionary of English.
The current editions in 2003 are sixth of the Oxford dictionary, fourth of the Longman dictionary, third of the Collins Cobuild dictionary, and most recently the second of the Cambridge dictionary. However, 2002 saw the entrance of yet another competitor: the Macmillan English Dictionary for Advanced Learners.