The first English monolingual learner's dictionary was The Idiomatic and Syntactic Dictionary of English by A. S. Hornby published in 1942. This 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 language teaching industry worldwide. It is now in its seventh edition as the Oxford Advanced Learner's Dictionary.
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, which has now become a standard feature of learners' dictionaries. 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. 2002 saw the entrance of yet another competitor: the Macmillan English Dictionary for Advanced Learners.
The current editions in 2008 are the seventh for OUP, the fourth for Longman, the sixth for Collins COBUILD, the third for CUP, and the second for Macmillan.