The very earliest dictionaries of English were actually glossaries that translated Latin words into Old English - the form of English spoken before about 1100 A.D.
The monolingual dictionary (one that lists English words and gives definitions in English) didn't appear until 1600 - so Shakespeare did much of his work without even the possibility of looking things up! For the first century or so, these dictionaries only defined hard words. It wasn't until the 18th century that dictionaries grew and included most meanings of even common words. During that century most of the features we associate with dictionaries first appeared, such as pronunciations, etymologies and parts of speech. In the nineteenth century dictionaries of English began to attempt to cover the whole vocabulary.
Large collections of examples of word usage were built up and used as the basis for the dictionary. In the twentieth century dictionaries became yet more inclusive covering slang, technical and regional language not previously admitted.
Dictionaries for different purposes and groups (for example pocket dictionaries and foreign learners' dictionaries) began to appear. With the advent of the computer it became possible to use computer databases as the source of language evidence alongside or instead of examples on file cards and eventually to publish dictionaries electronically on CD-ROM and online.